The film opens with Claude Gaspar being assigned to a new cell with 4 other prisoners. Their names are Manu, Geo, Roland, and "Monsignor", and they’re not a very friendly lot. They eye Gaspar warily and gently ask him questions about himself, and about the crime that brought him to prison. Gaspar explains that he wounded his wife during an argument, and since the gun was preloaded, he was charged with attempted murder. This admission seems to cause the 4 to relax somewhat, and Geo states "You are looking at 10 years." The full story eventually comes out. The four existing prisoners are in the midst of planning an escape, and they need to know if Gaspar will assist them. Staring at a long sentence, he agrees to help.
Many prison break dramas rely on elaborate plots and gimmicks to allow their protagonists to break out, but this one is a different animal. Quite simply, they will try to smash their way out of the cell, and in one brilliant, almost real-time sequence, they use a chunk of metal from a bunk bed to pound through a concrete floor. It’s hard work, and it LOOKS like hard work, as they take turns breaking the floor away, with no sounds except that of concrete giving way, and men panting from their exertion.
Breaking through the floor of the cell, of course is only part of the battle, and Roland and Manu go beneath the prison to scope out the rest of the work. Roland is plainly the brains behind the escape, and seems to have thought everything through. A small hatch door leads them to where they will need to go, but if they break it down it will be noticed. Roland comes up with a brilliant method of leaving the door intact while still allowing them to get through it. The final obstacle will be to break through the walls of the sewers below the prison, but this one will take quite a bit longer – a couple of days.
An interesting point to make here about "Le Trou" - The film has no interest in what the convicts have done (apart from Gaspard). There is the suggestion that Manu is in for murder and is scheduled to hang, but the film never really pursues it. Roland has certainly been behind bars before – It’s noted by Monsignor that Roland has broken out 3 or 4 times. It is pretty safe to assume that the entire group of four deserves to be in jail.
There is one interesting sideplot that comes up. Geo has been front and center in the digging, but tells Roland in a private moment that he isn’t going to escape with them. He states that his mother almost died when he was arrested, and that if the police show up at her door looking for him, that it might kill her. Geo’s sacrifice will take on a poignant irony at the films’ close.
Finally, the tunnel is ready, and the 5 make plans to escape that night. Gaspar receives notice that the superintendent wants to see him, and comes back to tell the others that his wife has dropped the charges against him. Manu notes "You were gone 2 hours – What did you talk about?" His inference is clear – Gaspar now has no reason to go through with the breakout, and may have betrayed them to the prison authorities.
A fragment of broken mirror attached to a toothbrush has been a useful tool to the 5 throughout the movie – They stick it through the peep-hole and use it to check the outside hallway. This same toothbrush now provides the films most memorable image, as it becomes clear just what Gaspar talked about for those 2 hours. Becker isn’t finished with the betrayals, however, and his last one is a doozy. Roland has the last word in this one, and his final line is laced with sarcasm, pity, hatred, and maybe just a tinge of gallows humor.