"Green for Danger" (1946)

Let's face it. The British are superlative at whodunnits. Those ingenious mind puzzles where some diabolical murder has happened and there are multiple suspects but everyone has an airtight alibi and it takes a whipsmart detective to figure out the clever (but improbable) solution. Many are often set in wealthy mansions, or grand hotels, or sumptuous trains or ocean liners. That's what makes this smart entry fascinating. It's the English countryside during WWII and a murder takes place in an Army hospital caring for the war casualties. All the suspects are the doctors and nurses, think "M*A*S*H meets Agatha Christie". Only this inspector is played by that rascally old scene-stealer Alistair Sim. He manages to inject bits of dry humor in between his interrogation of all the hospital personal played by a cast of first rate, veddy British thespians. There's even some thriller overtones as we see the murder happen (but of course not who the murderer is). The whole thing is deftly crafted by the director/writer/producer team of Sydney Gilliat and Frank Launder. A satisfying little mystery gem.