In a wartime emergency hospital near London, green-in the medical environment, the color of comfort, the color of hope-becomes the color of menace when a local postman, a casualty of a German bombing raid, dies mysteriously on the operating table. After a curious nurse meets an unhappy fate, Scotland Yard, in the person of Alastair Sim, arrives to investigate. Using understated ingenuity to unmask the killer, his droll wit neatly balances the edge-of-your-seat tension of this best of British thrillers-like its characters, deceptively pleasant, its rural setting a camouflage for much wickedness indeed. The charm of the film is its game: for ninety minutes we guess, while Sim's Inspector Cockrill does all the work.