In June 1941 a baffling Luftwaffe radio message mentioning a new invention with the codename Freya (the Viking goddess of love0 is picked up by the decoders of allied intelligence. Hermia Mount, a British intelligence analyst, suspects the existence of an experimental radar station on the coast of Denmark. Meanwhile, a young Harald Olufsen, a brilliant Danish student, has spotted an unusual installation near his island home. Unable to resist a challenger, Harald is soon drawn into Hermia's investigation, but when he finally learns the truth, he finds the only way of getting to England with the information is in a near-derelict hornet moth biplane, mouldering away in the nave of a ruined church.