In Spain, the former Nazi doctor Klaus tries to commit suicide jumping off the roof of his manor. However, he survives with the entire body paralyzed and dependable of an iron lung with glass sides. His wife Griselda decides to hire a nurse since she does not bear the situation. Klaus asks Griselda to hire Angelo, a mysterious teenager that appears in their house. Angelo befriends Klaus' daughter Rena and sooner it is shown that Klaus was a pedophile that loved to feel the fear of death in young boys before abusing and killing them. Further, Angelo is a disturbed and totally insane victim of his experiments that intends to follow the insanities described in Klaus' diary and incorporate his personality.

In the harsh post-war years' Catalan countryside, Andreu, a child that belongs to the losing side, finds the corpses of a man and his son in the forest. The authorities want his father to be made responsible of the deaths, but Andreu tries to help his father by finding out who truly killed them. In this search, Andreu develops a moral consciousness against a world of adults fed by lies. In order to survive, he betrays his own roots and ends up finding out the monster that lives within him.