When top-level scientist Arthur Vincenti (Alejandro Rey) suffers a nervous collapse, his military handlers fear he may be at risk of being kidnapped by a group of international terrorists who sell their victims to the governments of communist nations. Vincenti's psychiatrist, Dr. Bartholomew Snow (Rock Hudson), and fractious sister, Vicky (Claudia Cardinale), are drawn into a web of intrigue alongside the mysterious Fitzpatrick (Guy Stockwell), who claims Vincenti may already be an enemy agent.