Juan Oliver (Alberto Ammann) has just landed a job as a prison guard and to show willing, he turns up a day early for a tour of the facility.
During an inspection of the high-security cellblock, the inmates break free and a full-scale riot ensues.
Juan is trapped in the melee and thinking fast on his feet, he poses as a newly arrived prisoner, successfully pulling the wool over the eyes of top dog Malamadre (Luis Tosar).
One of Malamadre’s henchmen, Apache (Carlos Bardem), isn’t convinced and using a concealed telephone, he asks a snitch on the outside to run a background check on Juan.
Meanwhile, Juan’s pregnant wife Elena (Marta Etura) races to the prison desperate for news of her husband.
Inside the complex, hostage negotiator Ernesto Almansa (Manuel Moron) attempts to restore calm and to end the stand-off peacefully before Malamadre discovers Juan’s true identity.
By Damon Smith
Released: July 15 (UK, selected cinemas) (18, 112 mins)