A somewhat complex and extremely enjoyable mystery over who is stealing the advanced prototype aircraft all over the world. It derives from the premise that resulted in RDF/Radar, that of a beam which could stop engines in flight. A salvage ship of an un-named but Teutonic sounding power is conveniently present at each test site where an aircraft is lost, and it is up to Major Charles Hammond (Ralph Richardson) of the Air Ministry to discover the reason, he is assisted in this endeavour by Olivier as Tony McVane and alternately helped and hindered by his (Hammond's) sister Kay Lawrence played by Valerie Hobson. Complete with a shoot-out on the salvage ship, all is eventually well and consistently funny.
Directed by an American, Tim Whelan, and co-written by Jack Whittingham author of a couple of later James Bond scripts. Reputedly dialogue between the principals is full of ad-libs and improvisation.
Try to keep track of Major Hammond's umbrella, and his girlfriend.