Keraudy/Darbant is one of four cons who've volunteered for work making cardboard boxes in their shared cell. They're joined by a fifth prisoner, Claude Gaspard (Mark Michel), who's been transferred while his original cell is under repair. Claude faces an attempted murder charge for taking a shot at his wife. It's a he-said-she-said situation and doesn't look good for him. He may be desperate enough to be trusted with his new cellmates' secret. The pile of cardboard the guards have nicely brought in for them is going to conceal a hole they mean to dig through the cement floor of their cell. That should get them into the service corridors, and from there they hope to get into the sewer system and escape through a convenient manhole cover. Their cell is an enclosed room, and they'll do their digging by day, when the sound should be obscured by the other noises of daily routine. Claude ingratiates himself with his cellmates by sharing his food packages and joins in the step-by-step, day-by-day business of finding a way out of prison. He comes to respect the industrious cons and experiences an ironic kind of rehabilitation through labor, until word comes that his wife is going to drop the charges against him. He may be able to walk out the front door, but what does that mean for his new friends who plan an earlier exit?...
The view through a cell door via "periscope" -- a shard of glass mounted on a toothbrush. A typical instance of convict creativity in Le Trou.
Le Trou is a prison-break movie but not a crime film. Giovanni and Becker don't have a study of the criminal mind in mind. Instead, the movie is very much about the ennobling quality of work, even if that work contradicts the rehabilatory purpose of prison confinement. However bad the prisoners may have been on the other side, they demonstrate all the bourgeois virtues of teamwork and time-management as conspirators, even improvising their own hourglass so they can keep track of time while digging underground. They also demonstrate working-class solidarity, until the moment when Claude gets an exclusive chance at freedom. What happens later leaves you asking who the real criminals are.
Most of the commentary I've seen on Le Trou treats the film as some sort of response to a different kind of breakout movie, Robert Bresson's A Man Escaped. I haven't seen that film, though the comparisons make me want to do so. All I can say is that, on its own terms, Le Trou is one of the better prison-break movies that I've seen.