In pre-WWII England, advanced British aircraft prototypes carrying experimental and secret equipment are vanishing with their crews on test flights. No one can fathom why, not even spymaster Major Hammond (Ralph Richardson) or his sister Kay (Valerie Hobson), a newspaper reporter, who had been working undercover in the canteen used by the crews at the Barrett & Ward Aircraft Company. Major Hammond is seen as an outsider, but soon finds a friend in a star pilot, Tony McVane (Laurence Olivier). Hammond is convinced that Jenkins (George Curzon) the company secretary, is a foreign agent, but Jenkins is killed by gunmen before he can give up the names of his contacts. McVane carries out the next test flight. His aircraft, like the others, is brought down by a powerful ray beamed from a mysterious ship manned by a foreign crew. Although the nationality of the crew and agents aboard is unknown, they spoke with German accents. McVane and his crew are taken hostage aboard the ship, and what happens next is a thrilling ending! This is a vintage thriller not to be missed. (78 minutes - 1939 - Black & White - 4:3)