This is the kind of brisk, bright and thoroughly engaging comedy thriller that the British film industry has, sadly, forgotten how to make. But, then again, there are no more Alastair Sims to transform a passage of jovial banter into a moment of nail-biting suspense simply by slowing that melancholy Scottish accent and lowering those expressive oyster eyes. Gone, too, are such expert character actors as Leo Genn, whose ability to portray heroes and villains alike deepened the mystery in whodunnits such as this one, in which a patient is murdered on the operating table. Sidney Gilliat directs with a deliciously dark wit.

In the midst of Nazi air raids, a postman dies on the operating table at a rural hospital. But was the death accidental?