Humphrey Paxton, the son of one of Britain's leading atomic boffins, has taken to carrying a shotgun to 'shoot plotters and blackmailers and spies'. His new tutor, the plodding Mr Thewless, suggests that Humphrey might be overdoing it somewhat. But when a man is found shot dead at a cinema, Mr Thewless is plunged into a nightmare world of lies, kidnapping and murder—and grave matters of national security.