June, 1941 - and a baffling Luftwaffe message mentioning a new invention code named Freya is picked up by the decoders of Allied Intelligence. Hermia Mount, a British Intelligence analyst, suspects the existence of a experimental radar station on the coast of Denmark. Meanwhile, young Harald Olufsen, a brilliant Danish student, has spotted an unusual installation near his island home. Unable to resist a challenge, 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...