In England, an eccentric police inspector, an earnest test pilot and a spunky female reporter team up to solve the mystery of a series of test aircraft which have disappeared without a trace while over the ocean on their maiden flights; unaware, as they are, that a spy ring has been shooting the planes down with a ray machine hidden aboard a salvage vessel which is on hand to haul the downed aircraft aboard, crews and all.

A German submarine is sent to the Orkney Isles in 1917 to sink the British fleet.

Bob Stevens awakens in a hospital with a gunshot wound to his head, and is told that he has been in Paris for ten days. However, this cannot be true because he insists that he crashed his plane and has no recollection of being anywhere for ten days. Bob decides to follow a note found in his jacket, to the woman who wrote it, "Miss D", and get to the bottom of the whole strange situation.