When Sam is wanted by the police, he is supposed to be able to hide inside
buildings (but not on roofs or in stairwells that are visible from outside) in
order to evade arrest. However, because of a bug in the routine that checks
whether Sam can be spotted by the police in his current location (see 70D6),
Sam's attempts at hiding may be either futile or undeservedly successful. In
particular, if Sam is on the roof of or inside a building other than the hotel
(and not in a stairwell that is visible from outside), he will be invisible to
the police if he's facing right, but visible if he's facing left.
If Sam is wanted by the police, one place he can go and be certain that the
cops will not get him is the far right edge of the roof of the apartment
building next to no. 74. As soon as Sam reaches that spot - at coordinates
(23,6), to be precise - any policemen who are chasing him will turn round and
head for the top floor of the hotel instead.
The reason for this is that the region containing the roof of the apartment
building next to no. 74 is defined such that it extends only to x-coordinate 22
instead of 23, and the region adjacent to it (beginning at x-coordinate 23)
corresponds to the top floor of the hotel (see EFE8).
In addition, when the cops reach the top floor of the hotel, they will proceed
to the wall of the room on the far right and then freeze.
When Sam feels that the time is right to turn himself in, he can unfreeze the
policemen by approaching them. When he gets close enough, one of them will pick
Another place Sam can go and be certain that the cops will not get him is the
room above his office. First you'll need to get the hook (POKE
32745,64 while a game is in progress). Then go to the top-floor cyan
room in the apartments next to no. 19, call the police, hang up, go to the
right edge of the roof of the apartments, throw the hook over the roof of
no. 19, make your way across the rope to the roof of no. 17, and go down into
the room above Sam's office. Instead of following Sam there, the police will go
to Sam's office instead and run up and down continuously.
The reason for this is that the routine at ED8C assumes that every level of
a building is reachable by climbing staircases going up from the ground
floor. This is true for every building in the city except no. 17: there is no
staircase leading up to the top floor from Sam's office below. So the police
make their way to Sam's office only to find that there is no route up to their
Inside and out
Go to the far left of the room above Sam's office (to do which you'll need the
hook: POKE 32745,64) and turn round to face right; part of Sam's
sprite will appear outside the room.
Under the rope
After throwing the hook (POKE 32745,64 while a game is in progress
gives Sam the hook) over the roof of no. 19, cross the rope to the extreme left
edge of the roof of no. 17, turn round, and press 'A' ('down') or 'O' ('left')
twice - Sam will step down below the level of the rope so that his feet are
hidden. From here it's possible to walk below the level of the rope all the way
back to the roof of the apartment building.
This bug is caused by the location descriptors at B9E6. In particular, the
descriptors at B9EC (y=6) and B9EE (y=7) should not apply to x-coordinate
222. One way around this is to give x-coordinate 222 its own set of location
descriptors for y-coordinates 13, 19, 25, and 31:
If Sam stands on the right edge of the roof of the apartment building next to
no. 19 while the rope is there and both policemen are chasing him, one
policeman will pick him up, and the other will then walk onto the rope and
eventually get stuck at the right end, next to the edge of the roof of no. 17.
(POKE 32745,64 gives Sam the hook while a game is in progress, and
there is a phone in the far left room on the top floor of the apartment
building from which Sam can call the police.)
The key to reproducing this bug is to keep the policemen at bay until both of
them have spotted Sam on the edge of the roof and are heading there to catch
him. This can be done by stepping off the edge of the roof and onto the rope
(which makes a chasing policeman turn round and head the other way), staying
there for a few seconds, and then turning round and stepping off the rope and
back onto the edge of the roof (which makes a chasing policeman turn round
again and head for Sam's location).
Using this technique, Sam can keep one policeman busy until the other shows up,
and then allow himself to be arrested.
The non-arresting policeman proceeds to the edge of the roof even after Sam has
been arrested because of a quirk in the routine at 72B1, which makes the
policeman complete his journey to the spot he was heading for while chasing Sam
before resuming normal patrol duty on the sidewalk.
But why doesn't the non-arresting policeman then simply step down from the edge
of the roof and return to the sidewalk? Here is where the story gets
The policeman is standing at (206,6,1) (on the top-right edge of the roof),
facing right. His destination is somewhere on the sidewalk or road. Under these
conditions, the routine at ED8C returns with A=4 (go down) at
EE62. The routine at F600 takes this return value and jumps to the
routine at EBA0. This routine then moves the policeman forwards (and
therefore onto the rope), because there is no step going down at (206,6): the
location descriptor for (206,6,1) at C3F5 says 'left, right' only.
The policeman keeps moving forwards in search of a way down, until he finds one
at the right end of the rope, and takes it. With the policeman now at
(221,7,1), the routine at ED8C returns with A=1 (go right) at EE5B,
because his x-coordinate (221) is less than the x-coordinate of the top of the
staircase leading down to the floor below (236, as defined by the third byte of
the region identifier entry at EFFC; this is the staircase leading down from
the roof of no. 17 to the room above Sam's office). Then the policeman turns
round, heads right, and gets stuck at (222,7,1), because the only available
direction at that location is left (as defined by the location descriptor at
Note, however, that the policeman who gets stuck in this way can still arrest
Sam (if Sam later becomes wanted by the police, and tries to make his way
across the rope). If that happens, Sam gets stuck too, and the game is
The plight of the non-arresting policeman (2)
Further evidence that policemen and roofs don't mix can be found on the roof of
the apartment building next to no. 74. If Sam stands in the spot just to the
left of the right edge of this roof when both policemen are chasing him, one
policeman will pick him up, and the other will then pace up and down the roof
continuously, unable to find his way back to the sidewalk and regular patrol
(There is a phone in the right-hand magenta room on the third floor of the
apartment building from which Sam can call the police.)
Again, the key to reproducing this bug is to keep the policemen at bay until
both of them have spotted Sam near the edge of the roof and are heading there
to catch him. This can be done by stepping towards the far right edge of the
roof (which makes a chasing policeman turn round and head the other way),
staying there for a few seconds, and then turning round and stepping back to
the spot just to the left of the edge of the roof (which makes a chasing
policeman turn round again and head for Sam's location).
So what prevents the non-arresting policeman from returning to the sidewalk
after Sam has been arrested in this case? As noted in the previous bug, there
is a quirk in the routine at 72B1, which makes the policeman complete his
journey to the spot he was heading for while chasing Sam before resuming normal
patrol duty on the sidewalk. So first of all, the policeman heads for (22,6),
just to the left of the top-right edge of the roof. Unfortunately, however, he
never makes it there.
Before any character can reach the location at (22,6), he must first pass the
location at (21,7). When the policeman reaches that spot, the routine at
ED8C returns with A=2 (go left) at EEAB, because his x-coordinate
(21) is greater than the x-coordinate of the bottom of the (non-existent)
staircase leading to the floor above (20, as defined - incorrectly - by the
fourth byte of the region identifier entry at EFE8). Therefore the policeman
turns round and walks left instead of stepping up onto the top edge of the
Then, when the policeman reaches (19,7), the routine at ED8C returns with
A=1 (go right) at EEA9, because his x-coordinate (19) is now less than
20. Therefore the policeman turns round and walks right, back to (21,7). And so
on and so forth, until Sam is once again wanted by the police, and the
policeman's destination changes to wherever Sam is.
When Sam's score hits 50, the first phone message from Lana (message
0x3B: LANA ANSWERED 'OOH SAM! THEY KILLED MY FIANCE AND STOLE THE
BUDGIE') is activated (see 5FF9). However, if Sam calls Lana (on 7162) from
the phone in the third-floor magenta room in the apartments next to no. 74
while the room past the catwalk is on-screen, no one answers.
The reason no one answers is that (a) a phone in a room that is currently
on-screen will be answered only if a character is nearby (see 772F), and (b)
Lana's phone is the one in the room past the catwalk (see 6B00).
Hook v. bird
When Sam phones Lana while in possession of the budgie, he should receive the
message 'LANA ANSWERED 'OOH SAM! YOUVE GOT THE BIRD. SEE YOU IN YOUR
OFFICE''. However, if Sam phones Lana while he has both the hook and
the budgie, he will get no message; this is because the event table entry at
60BB checks that Sam has the budgie and only the budgie. (POKE
32745,192 gives Sam the hook and the budgie while a game is in
In game mode 4 - after Lana has been put in jail and the mob is after Sam - Sam
can call 999 and hear the message 'OK CRUISE WE'RE COMING'. However, no
policeman ever arrives, because there are no police on patrol duty in game mode
Sam must have at least $46 when he's arrested, otherwise the game will end
immediately (see 7B9A). In addition, if Sam has $20 or less when the jailer
comes to let him out of the cell, the routine at 7B6A will enter an infinite
loop by trying to find a bail amount of $20 or more that Sam can afford,
effectively ending the game and sentencing Sam to a life of suspended animation
But can this actually happen? Is it possible for the jailer to come down from
his office too late to save Sam from a life sentence? Let's do the maths and
First, let's assume that Sam does have only $46 when he's arrested, and that
he's arrested in the location that is farthest from the police station: the
roof of the apartment building next to no. 74. It takes the arresting policeman
about 1m14s to get to the jail cell (with Sam) from that location. Since Sam
loses a dollar every 5.12s (see 7AB6), that means he will have no more than
$32 left by the time he's dropped off. And 1m2s later, he will have no more
than $20 - the critical amount. The question thus becomes: is it possible for
the jailer to take more than 1m2s to come down and let Sam out?
The jailer's routine involves walking up and down in his office for a while,
going down to the cell to let Sam out (if he's there), going back up to the
office, and starting all over again. The number of walkabouts he performs will
be anywhere from 32 to 63 (see F748). Each walkabout consists of walking to
a randomly chosen spot that is 6, 4, 2 or 0 x-coordinates to the left of the
walkabout origin. Travelling one x-coordinate requires two movements. So the
number of movements the jailer will make while walking up and down in his
office could be as high as 63*12=756, but will be 47.5*5=237.5 on average.
Now to translate that into actual time. The character-moving routine at F1FC
moves three characters at once, and there are 16 characters to be
moved. Therefore each character is moved on one in every 5.33 passes through
the main loop when running, and one in every 10.66 passes when walking. Passes
through the main loop are made at least 0.02s apart, so a walking character is
moved once every 0.21s. This means that the jailer could spend as much as
756*0.21=158.76s walking up and down in his office, but will on average spend
237.5*0.21=49.875s doing so. To those figures we would need to add the time
taken to walk down to the jail cell from the office.
So it is possible for the jailer to spend too long in his office before coming
down to let Sam out. Unlikely, but certainly possible.
Post-traumatic teleportation disorder
When Sam knocks a character over by landing on his head from above, that
character is supposed to:
(1) drop to the the floor and remain there for a brief period
(2) stand up and stagger around for another brief period
(3) walk back to the spot where he was hit on the head
(4) resume whatever he was doing at the time he was struck
But because of a bug in the routine at FA83, the walking back part of step
(3) is omitted. Worse than that, if the character was midstride at the time of
the collision, step (3) is replaced by an immediate teleportation to the
character's pre-knockout, post-midstride coordinates. As a result, you might
see the recovering character zip from A (the point where he stops staggering
around) to B (the spot just to the left or right of where he was hit on the
head) without passing through the intervening space.
If Sam moves midstride just before being picked up by a policeman, then he can
escape from the jail cell after being dropped there by the simple act of
turning round (to face right). As soon as he does that, he will teleport back
to the spot where he was arrested.
Whenever Sam (or indeed any character) moves midstride, his post-midstride
animatory state, x-coordinate and y-coordinate are calculated and stored in
bytes 0x05, 0x06 and 0x07 of his buffer by the section of code at EC07, to be
retrieved later (usually soon after) by the routine at EC5A. However, if Sam
is picked up by a policeman while he's midstride, his post-midstride movement
is delayed. When 'P' is pressed after he's been dropped in the cell, the
routine at ECDC is called, which first turns Sam round (because he's facing
left). Then that routine jumps to the code at ECE4, which detects the
post-midstride y-coordinate stored in byte 0x07 of Sam's buffer, and accordingly
sets the midstride timer in byte 0x09 of his buffer to a non-zero value. A few
passes through the main loop later, the midstride timer is decremented to zero
by the code at F069, and Sam is belatedly moved to the post-midstride
coordinates that were calculated just before he was arrested.
The following POKEs fix this bug by making sure that Sam's post-midstride
y-coordinate is cleared when he's picked up by a policeman:
Note that the midstride trick does not work with gangsters, because the code at
FBA6 sets byte 0x07 of Sam's buffer (which holds his post-midstride
y-coordinate) to zero when he lands after being dropped off the roof of a
building. To enable the midstride trick to be used with gangsters:
Now when Sam turns round after coming to, he will teleport back to the spot
where he was picked up by the gangster.
The persistent sniper
It's possible for part of the sniper's sprite to remain on screen after the
screen has scrolled the sniper's body out of view. To see this, go to the first
floor of the apartments next to no. 19, and position Sam so that the doorsteps
of no. 19 are visible on the left side of the screen.
When the sniper appears on the left side of the doorsteps, move Sam left so
that the screen scrolls right. The brim of the sniper's hat and maybe also his
gun will remain visible at the right edge of the screen until wiped away by
other characters passing by on the sidewalk.
The conspicuous sniper
One of the defining characteristics of a sniper is that he should remain
concealed or inconspicuous when aiming at his target. However, because of a bug
in the sniper-controlling routine at 621E, the sniper will, after emerging
to take aim, remain brazenly out in the open for all to see until Sam gets too
close. The apparent intention of the sniper-controlling routine is that the
sniper should emerge, shoot once or twice, and then hide again when byte 0x10
of the sniper's buffer has been decremented to zero from its original value
between 0x0A and 0x19 (see 62DB).
No. 19 lockout
It's possible to lock the gangsters at no. 19 out of their house, leaving Sam
free to enter via the roof and explore the mob stronghold with impunity. To
achieve this feat, proceed to no. 19 and stand on the right edge of the front
When the door opens, the gangsters will walk out onto the doorstep and then
freeze, as if uncertain where to go next to grab Sam.
If Sam then goes back down to the sidewalk, the gangsters will unfreeze and
start knocking on the front door - but because there's no one at home to answer
it, they'll never get in.
If, on the other hand, Sam approaches the gangsters on the doorstep, one of
them will pick him up with the intent of carrying him to the roof, but will
instead get stuck at the front door, unable to get in.
The reason that the gangsters freeze on the doorstep of no. 19 is a combination
of a quirk in the routine at ED8C (which determines the next move a
character should make to reach his destination), the boundary of the inner
region that is watched by the gangsters (as defined at FD44), and the logic
in the routine at 7A82 (which controls a gangster who is chasing Sam). When
a gangster arrives at the front door his coordinates are (211,31,1) and Sam's
are (212,31,2). The routine at ED8C then sends the gangster down a step to
(210,32,2) instead of simply turning him round and changing his z-coordinate
from 1 to 2. But (210,32,2) is outside the inner region watched by the gangster
(which extends only to y-coordinate 31), which means the routine at 7A82
will abort without moving the gangster anywhere while Sam remains inside the
POKE 62177,136: POKE 62178,144 (to give each gangster a
key to no. 19)
POKE 64839,33: POKE 64843,33 (to extend the inner region
and prevent the gangsters from freezing on the doorstep)
The gangsters at no. 19 are not the only ones who can become confused and
freeze while chasing Sam: the gangster who watches for Sam outside the police
station in game modes 2 and 3 is susceptible to the same trick as well.
To see this, Sam first needs to get to the right edge of the police station
steps, just above the sidewalk:
(Sam can get here without being caught by the gangster either by going via the
roof of no. 27 - assuming he has the key to that house - or by calling the
police and enduring a brief stint in jail first.) When the gangster is beyond
the left edge of the police station steps, step down onto the sidewalk, and
then quickly back up onto the police station steps. The gangster will follow
Sam onto the first step above the sidewalk and then freeze:
The gangster will remain frozen until Sam leaves the outer region
(0<=x<255, 10<=y<36) by going to y=9 (between the 4th and 5th
floors of a building). It's possible for Sam to run past the gangster (towards
no. 31 on the left) while he's frozen without being picked up, but this
manoeuvre requires perfect timing that's impossible to judge from just watching
the screen, and will fail more often than not.
An urgent message delayed
The routine at 75D0 is supposed to determine the amount of time for which
the current message (or message portion) should remain on screen before the
next one is displayed. This interval is normally 2.56s, but is reduced to 0.64s
if an urgent message has been queued (see 75CA). However, if the urgent
message number is stored at a lower address in the 8-byte message queue at
7FB8 than the number of the message currently being displayed, the routine
at 75D0 will fail to find it, and so messages will continue to be displayed
at normal speed. To demonstrate this:
1. When a new game starts, the message index (held in bits 0-2 at 7FB7)
is 3; increase it to 7 by picking up a phone and hanging up twice.
2. Pick up a phone other than Sam's, dial 7337, and wait for Daisy to
start relaying the message to Sam; now the message index is 7 (again).
3. While Daisy is relaying the message to Sam, quickly hang up and then
press 'J'; this queues an urgent message (see 6177) with index 0, which is
less than the index of the message currently being displayed (7).
4. Note how the game pauses, but the message from Daisy continues to
display at normal speed, until finally 'JOYSTICK?' appears.
Blank tiles behaving badly
The knocked-out sprites for certain characters contain blank tiles that should
The reason for this is that the routine at F928, which prepares the tiles
for a knocked-out sprite by making rotated copies of tiles 0x01-0x04 and 0x06-0x09
of the character's base sprite, needlessly makes rotated copies of blank tiles
(those with a tile reference of 0x00) too. However, the blank tile (the graphic
and mask data for which are located at addresses C700 TO D600 STEP 256)
does not contain the correct mask data - it is all zeroes instead of 0xFFs.
This is not normally a problem because the sprite-tile-printing routine at
E8F3 is optimised to ignore sprite tiles with a tile reference of 0x00. But
the rotated copies of the blank tile have non-zero tile references, and are
This bug is noticeable if Sam knocks over one of the affected characters on the
sidewalk: the blank tiles will obscure parts of the building (and possibly
other characters) behind the stunned character, as shown here where Sam has
just landed on Daisy after being dropped from the roof of no. 19:
The simplest fix is to set the mask data for the blank tile to all 0xFFs:
Another fix (which leaves the graphic and mask data for the blank tile
completely unused) is to set the relevant tile references in the affected
sprites to 0x00:
The icon for the ringing telephone is perhaps not as it should be. Note how the
business end of the earpiece is 3 pixels long, compared with 2 pixels when the
phone is not ringing:
However, this is probably not a bug in the graphic data itself. If the routine
at 6FF4 is modified so that it copies the otherwise unused two bytes of
graphic data (which correspond to the earpiece) from 7043 to the screen, the
ringing telephone icon looks like this instead:
When Sam hits the ground after being dropped from the roof of a building by a
gangster, the portion of the screen containing the play area (that is, the top
20 rows) is scrolled up and down seven times, with an accompanying sound
effect. On each upward scroll, the 20th row of the screen is supposed to be
replaced by a solid blue line (attribute value 9). However, because of a bug in
the scrolling routine (see FC6A), instead of the 20th row of the attribute
file being POKEd with 9s, the top pixel line of the 20th row of the display
file is POKEd with 9s, which produces quite a different - and visually jarring
When Sam moves up from the sidewalk onto the front steps of a building, his
z-coordinate remains at 4 instead of changing to 2, which means that people
walking past on the sidewalk below will be drawn behind him instead of in front
The reason for this is that the location descriptors for z=4 (see C400) that
correspond to the front steps of buildings don't have bit 0 or bit 1 set to
indicate that a z-coordinate transition should occur, and so the section of
code at EBF4 leaves Sam's z-coordinate unchanged upon climbing the step.
Conversely, the location descriptors for z=4 that correspond to the places
where there is a step up from the road to the sidewalk (at x=7, 14, 164 and
198) do have bit 0 or bit 1 set. So when Sam moves up from the road to the
sidewalk, his z-coordinate will change from 4 to 2, which means that other
characters on the sidewalk will be drawn not behind him (as is the norm) but in
front of him.
After Sam has collected the hook from no. 74, an immobilised banknote can be
seen on the sidewalk outside that building or the hotel. The banknote can be
somersaulted onto repeatedly (to gain extra cash) without disappearing.
The reason this happens is that the routine at 634C brings the banknote out
of service when Sam collects the hook - thus leaving character buffer 0xE5
available for use by the hook when it's thrown - but doesn't remove the
banknote from view.
Run, gangster, run
Approach the gangster on the catwalk from the left, and stop at the point where
moving right once would make the gangster starting chasing Sam (who is shown
outside here for clarity):
Now quickly take one step right, and then turn round and run up to the roof of
the apartment building. After briefly chasing Sam, the gangster will return to
the catwalk, but now he is running continuously instead of walking.
The self-modifying data table
The first entry in the data table at 8128 in the loader code results in
817D being POKEd with 0x86 (replacing the original contents: 0x7C); but
817D is in the data table itself, and corresponds to address D380, which
means that D380 ends up being POKEd with 0x86 instead of 0x7C, thus
leading to the graphic glitch Lana's waist.
POKEing 817D with 0x86 is actually redundant, since 817D is in an area
of memory that is overwritten soon after loading (817D contains the LSB of
the operand of the 'LD ($8086),A' instruction at 817C in the
This bug is not present in the re-release of Contact Sam Cruise by Summit
Software in 1988, which uses a different loading scheme.
Tricks with light switches
Some light switches are accessible in places they're probably not supposed to
be: when flipped, they affect lights in places other than where the
light-switch-flipper is standing.
For example, go to the right-hand side of the shop underneath no. 17 and flip
the light switch - it switches on the lights on the second and third floors on
the right-hand side of no. 17.
Now go into the door of no. 17 and move as far right as you can; flip the light
switch there and the light in the shop underneath no. 15 comes on.
This time, go into the door of no. 17 and move as far left as you can; flip the
light switch there and the light in the shop underneath no. 17 comes on.
When the screen scrolls left or right as Sam moves through the play area,
certain members of character groups 0xD7-0xDD are moved in and out of
operation, depending on the portion of the play area that is visible. In
particular, the lady in a hat who is a member of character group 0xD7 is in
operation only when the far left edge of the play area is on screen (see
FEAE). That is a rather small range of operation - so small, in fact, that
it's possible to see her move out of operation (and become motionless) when the
left edge of the play area scrolls out of view:
1. Go to the right-hand magenta room on the third floor of the apartment
building at the far left of town.
2. Stand at the location such that moving right once will scroll the
screen left (see the image below).
3. Wait until the lady in a hat in the room on the left on the same floor
is at the rightmost extremity of her orbit, so that she is partially visible in
the stairwell (see the image below).
4. Quickly move right so that the screen scrolls left before the lady
turns round and heads back into the room.
5. Note that the portion of the sprite of the lady in a hat that is
visible in the stairwell remains visible but motionless either until it's wiped
away by another character moving past it, or until the screen scrolls right and
the lady starts moving again.
Like the displaced dame described above, the man in a bowler hat who is a
member of character group 0xDD and walks up and down on the second and third
floors of the apartment building next to no. 19 can be seen becoming motionless
when the screen scrolls too far to the right:
1. Go to the road outside the apartment building next to no. 19 and stand
at the location shown in the image below such that no part of no. 27 is visible
on the left.
2. Wait until the man in a bowler hat comes into the cyan room on the
second floor of the apartment building and is visible through one of the
3. Quickly move left so that the screen scrolls right (bringing the
traffic lights and the left side of no. 27 into view).
4. Note that the man in a bowler hat remains visible but motionless
through the window.