In the midst of World War II, a detachment of German soldiers led by Captain Klaus Woermann is assigned to guard a mysterious and ancient fortress nestled in the Carpathian Mountains. They are cautioned about the keep's hundreds of nickel crosses embedded in the stone walls. Ignoring warnings, two soldiers inadvertently unleash a malevolent force from within the structure. As inexplicable deaths begin to plague the garrison, the panic-stricken soldiers are thrust into a struggle for survival against an unknown entity with terrifying capabilities. Desperate to contain the situation, the Nazis bring in Dr. Theodore Cuza, a Jewish historian and professor, to unravel the secrets of the fortress.

Upon his arrival with his daughter Eva, Dr. Cuza becomes increasingly obsessed with discovering the nature of the evil within the keep. The presence of a mysterious stranger named Glaeken Trismegestus further complicates matters. He seems to possess deep knowledge about the entity and might be key to overcoming the menace. As the fortress's dark secret is slowly unraveled, allegiances shift, and motivations are questioned. With time running out, it becomes apparent that something ancient and powerful has awakened, threatening not only those within the keep but potentially reaching far beyond its confines. The struggle between humanity and this unleashed force intensifies, clouding lines of good and evil against a foreboding backdrop.