During a yachting trip, Nikos Karamanlis is stranded at sea with his pregnant wife Martha and their daughter Vicky. When Vicky dies from injuries sustained as their boat sinks, Nikos proposes cannibalizing her body to survive; Martha objects violently, and during the struggle she is accidentally stabbed by Nikos. He goes on to consume both his wife and his daughter, a choice that lets him endure long enough for his raft to drift back to his hometown — a quiet village on the outskirts of Borgo San Lorenzo in Tuscany, Italy. The weight of what he did gnaws at him, and guilt drives him into a cavern, where he retreats from the world and begins to transform into something monstrous.
Haunted by guilt, Nikos retreats to a cave and becomes a serial killer, aided only by his sister Irena, whose help is reluctant at best. He systematically wipes out the village and then turns his appetite toward outsiders, setting his sights on a vacationing couple, Mary and Stuart, and two campers named Hank and Allan. Outside the village, Mary’s group—Georg Stockmann, Rita, Marc, Vincent, and Caroll—face trouble with their RV. They find it abandoned except for scattered corpses, Mary’s blind sister Auriet, and Irena, who, fleeing Georg, leaves behind a chilling message: “Go away.” Nikos then kills Vincent, drags Caroll back to his cave, and moves the RV to a new place, while Irena commits suicide in front of Georg, Rita, Marc, and Auriet.
Georg discovers Nikos’s journal, and just as he begins to read, Carroll’s husband, a surgeon named Stan, arrives in the village and teams up with Marc to search for Carroll. Nikos kills Marc and confronts Stan and Carroll in the cave, where he reveals his traumatic past and then murders them, tearing Carroll open with a rock and devouring both Carroll and Stan’s unborn child. He also kills Auriet and Rita, and a brutal confrontation with Georg follows. After Georg shoots Nikos several times in the torso, Nikos spirals into madness, tearing out and gnawing on his own innards before attempting to drown Georg. As he dunkes Georg in a pool, visions of Martha haunt him, and Georg ultimately overpowers him, beating and decapitating him with a shovel as the suicidal Nikos pleads, > release me.
An unknown amount of time passes, and an Interpol agent named Doctor Steven Bauers is brought to Nikos’s cave after two colleagues claim Georg is still at large. Bauers finds Georg’s cellphone and Nikos’s journal — the latter chronicling everything up to the moment Nikos was killed by Georg. As Bauers wonders how the journal ended up in the cave and who added the later entries, he is suddenly shot in the face by an unseen assailant, presumably Georg.
