In Istanbul, a young woman is attacked by six thugs and the agent Frank Milland who had set a rendez-vous with her, is outnumbered, and she dies. Frank is menaced later in order to stop his inquiry about the thugs identities. Each clue he follows leads to more and more danger. Then he comes across Eva, a young woman who is the dead girl's spitting image; either she is her twin sister, or the woman who died in his arms. Eventually he encounters a mad sculptor, who is more than he pretends to be. Frank ends up a prisoner is an abandoned castle hidden in Turkey's mountainous hinterland, trying to save his own life and to prevent the development of a mysterious weapon that would put an end to civilization as we know it.