Impossible Mission

01 · What the code keeps

A phone that dials real tones, and a clock that runs slow in Europe

Found in the code	Where
Every game carves a new map out of solid rock: the 32 rooms are shuffled and dropped onto a grid of nine columns joined by eight lift shafts.	The stronghold
The phone on the pocket computer dials one of two numbers in genuine touch tones.	Sound and speech
The game counts 60 frames to the second. On a European PAL machine the six hours take 7 hours 12 minutes; only the lip-sync of the ending is corrected.	How it works, The ending
The four pieces of a puzzle divide its picture exactly. Descriptions of the game say they overlap.	How it works
The speech data holds eight voice lines, and the game never plays one of them.	Sound and speech

02 · Copy protection

Secret: two protection checks keep running during play

Most protection runs once, while the game loads. This game carries two more checks into the game itself, and each would stop a copy that slipped past the loader.

Check	What it does	Evidence
The disk	The program on the disk is broken in three bytes. The loader asks the drive about the disk, and only a good answer writes the correct bytes in. A copy that fails crashes once loading finishes.	`$C300`; the loader is described on the About tab
A chip register as an instruction	The start-up writes `$60` into CIA 2's data direction register B at `$DD03`. `$60` is the opcode of `rts`, and the game's delay routine calls `$DD03` as a subroutine on every pass.	`$7F6D`; tested: 47,272 calls in 120 frames, and a crash when the register holds anything else
A colour the loader left	The loader's last stage sets a background colour register, `$D024`, to `$0A`. Every frame the interrupt checks it, and if it has changed it jumps into the middle of an instruction where the byte `$02` halts the processor.	`$84FA`; tested: the machine froze at `$799A` within 30 frames

wait_ticks   clc
$7F6E        adc $E0        ; the frame counter
$7F70        jsr $DD03      ; CIA 2's register, holding $60: rts
$7F73        cmp $E0
$7F75        bne $7F70

The first instructions that set up $DD03 no longer exist by the time the game is running. The start-up clears its own first 17 bytes in the same loop that clears the sprite registers, so a memory dump taken during play shows zeros where the setting-up was.

03 · The copy studied here

The Epyx disk for European machines, with its protection intact

These pages describe one copy: the Epyx disk for PAL machines, imaged at the level of the disk's magnetic encoding, so that its protection still works. The loader asks the drive about the disk, and the program it loads is broken in three bytes until a good answer mends them (above). No version number or build string was found in the program.

Descriptions of the game used here come from the summaries of web searches made on 1 and 4 October 2026, when the pages themselves could not be opened, and from Wikipedia and magazine scans on the Internet Archive read on 6 October 2026. Each one was checked against the code, and the About tab lists them with what the code says.

The Source code tab links every explanation to its address. No game image is hosted here.

04 · Checked against the descriptions

Where the code and the descriptions disagree

Descriptions of the game, read in web search summaries on 1 October 2026, make claims that the code settles.

The claim	What the code does
The pieces of a puzzle overlap, so three can fit before you find you must start again.	The four pieces divide the picture exactly, and only their common frame may overlap (`$B180`, `$8037`, How it works).
There are six speech lines.	The data holds eight, and the game plays seven of them (`$BED9`, Sound and speech).
The stronghold has 31 rooms, or 32.	32 room records, two of them the code rooms (`$0E70`, The stronghold).
A cheat site: `POKE 26831,169` for a cheat mode, and four pokes for no opponents.	In this copy 26831 and 27028 are inside the agent's sprites, 31005 is in the routine that flips a piece, and 21006 is in the room character set. The pokes must be for another version.

05 · Open questions

What these pages have not settled

The words of the eight voice lines. The Sound and speech tab plays them; nobody has transcribed them.
The code rooms' puzzle was read in the code but not played.