They were all drawn to the keep. Tonight, they will all face the evil.

Set during World War II, a German army garrison is sent to guard a mountain pass in a village in Romania’s Carpathian mountains and sets up barracks in an ancient stone fortress. Two of the soldiers unwittingly release a mysterious entity that kills or corrupts those within its influence, drawing the attention of a Gestapo commander, a Jewish scholar and a mysterious traveller.

A highly skilled jewel thief, Frank (James Caan) longs to leave his dangerous trade and settle down with his girlfriend, Jessie (Tuesday Weld). Eager to make one last big score in order to begin living a legitimate life, Frank reluctantly associates with Leo (Robert Prosky), a powerful gangster. Unfortunately for Frank, Leo wants to keep him in his employ, resulting in a tense showdown when he finally tries to give up his criminal activities once and for all.