Even before his first official day on the job in a Spanish prison, a newly hired guard (Alberto Ammann) is trapped in a cellblock ruled by a charismatic killer with nothing to lose by killing again. The riots are soon on TV; SWAT teams and negotiators are called; the public is clamoring at the gates for news of their loved ones inside. The quick-witted guard passes himself off as an inmate, using his intelligence and neat penmanship to become the right-hand man to the ringleader (Luis Tosar), therefore distrusted by other inmates. Meanwhile, the prize hostages turn out not to be the wardens, but Basque members of the ETA terror group; if they're harmed, we learn, Spain's whole federal structure would be at risk. Though it lays on a few soap-opera twists (the guard's wife is pregnant, natch), Daniel Monzón's tense, superior drama places you in the agitated center of an unpredictable mob. There are good men and bad men on both sides of the prison bars, and none—not the cops, and not the cons—seem capable of controlling the urge toward violence. (The film sometimes recalls Paul Greengrass' Bloody Sunday in its street-level chaos.) If the guard succumbs partly to Stockholm Syndrome, bonding with his brutish comrades, he also sees the evils of those who were to be his future colleagues. During his first fateful visit, a warden warns him to never trust the inmates; later, he realizes the same advice applies in the other direction.