A Shudder on the Skin (1966)

The secretary of a professor in charge of a super-secret nuclear project, Susy Martin, mysteriously disappears. Her fiancée, Rick Dorsey, turns to a childhood friend, Frank Potter, who is now a private detective, to help him find her. The detective and his assistant / journalist / girlfriend/(cook) Margaret (the real ace up his sleeve!), while the police are misled by mysterious intrigues and the counterespionage itself are barking up to the wrong tree, manage to solve the case... but not without the support of the repentant Dr. Kerriman. Furthermore, an unexpected ending, just not to make it too trivial!