A British lady entomologist travels to a Balkan country to look into germ warfare trials using various bugs as carriers.

When British Intelligence discovers that an Iron Curtain country is developing insects as weapons, they persuade eminent entomologist Frances Gray (Margaret Lockwood) to get into the country to collect some specimens. On arrival, her cover is almost immediately blown and her contact murdered. The future looks grim for her and also perhaps for the world.—J-26