Margaret Lockwood is a scientist ("Frances Gray") who is asked by the British government to travel to the Balkans to discovers whether the communists there are trying to weaponise the humble fruit fly! Initially nervous, she takes courage from a radio serial that she listens to for her young nephew, and is soon embroiled in some espionage shenanigans with American journalist "Casey" (Dane Clark) as they try to get hold of one of these critters to return to the UK for evaluation. Local commandant "Razinski" (Marius Goring) cottons on quite quickly that something is afoot, but can the two complete their mission before he puts them up against a wall? Clark is a bit weak, here - but Lockwood and Goring work well together to make for quite an enthralling cat and mouse adventure that is peppered with some humour and a gentle swipe at red tape at the end. A few characterful contributions from Naunton Wayne and Wilfred Hyde-White help it along too. The production is a bit cheap and cheerful, and it plays a little to cold war politics, but I still quite enjoyed it.