Juan Oliver is deeply in love with his wife Elena, they are newlyweds and are expecting a child: when he passes the public exam to become a prison officer, he sees it as his chance to raise a family. Trying to cause a good impression, he reports for work one day early. Two colleagues show him around the old prison, telling him about the rough work and about Apache, a Russian informer. All of a sudden, and due to some building work, some plaster falls from the ceiling and hits Juan, who passes out. The guards take him into cell 211, which is empty, to try and revive him. But, as luck would have it, that's when a riot breaks out at the high security FIES cell block, the one that houses the most dangerous inmates. Juan's colleagues run away, leaving him stranded. When he wakes up in the cell he takes stock of the situation: if he wants to save his skin, he must pretend to be a prisoner.