The Cat Gang is a group of precocious British kids. They have a habit of hanging around a grown-up customs official who wishes that they'd beat it. But the Gang comes in handy when a smuggling gang arrives on the scene.

The efforts of test pilot John Mitchell to make a better life for his wife Mary and their two children seem doomed to failure and he blames himself. At the Conway Aero-Manufacturing Company of Wolverhampton, Mitchell is to take the company's new rocket-propulsion transport plane up for tests, fully loaded and carrying two important passengers - Ministry official Crabtree and buyer's representative Ashmore. Mitchell learns from his boss, Reg Conway, that if Ashmore does not recommend the plane, the company will be out of business and Mitchell out of a job, since the plane is not even insured as the firm's entire capital is tied up in the plane. Aloft, an engine catches fire and the passengers and other crew bail out, but Mitchell refuses to obey orders to jettison the plane in the Irish Sea.

When Germany invades Holland in 1940, a British intelligence officer and two Dutch diamond merchants go to Amsterdam to persuade the Dutch diamond merchants to evacuate their diamond supplies to England.

Jewel thieves, murder, and a manhunt swirl around a sailor off a cargo ship in post-war London.