A complicated story with many undercurrents to it, that are not plainly visible to the eye - a viewer might get confused by this intrigue, the main character being very difficult to understand. Only if you know something of the second world war and its experiences, the character that Robert Preston impersonates becomes credible.
It's a very different espionage story to the usual ones. Preston is a code breaker expert and has been through quite a lot in the war, and so has his wife - you never get really into her story, but it's clear she has gone through some very difficult ordeals. For that reason, and many others, he loves her more than can be expressed, and the first part of the film with their relationship is beautifully illustrated by excellent music reminiscent of a Rachmaninov symphony. The music by Frank Spencer is outstanding throughout. When the cloudburst occurs the upsetting shock is really unsettling, especially to Robert Preston, and the romantic film turns sinister and the more so for each new turn of events.
The main asset of the film is the very skillful story, which is more than intelligent, and you can't help admiring Robert Preston's character for his astuteness in managing his own intrigue. He surprises you all the time by constantly knowing more than the audience and thus leads the way into his own abyss, which is unavoidable - he admits it himself, and the audience accepts it, that he is already hopelessly a dead man for his atrocious loss.
It's as good a spy story as any of the great ones by Hitchcock and Carol Reed, only this is so much more sinister.