Shopkeeper's assistant Harry Jones is caught up in a whirlwind of crime when two crooks come looking for information.

They're trying to track down Professor Pureheart in order to relieve him of a top secret formula he's devised, and the gullible Jones is their best lead to locating the eccentric scientist.

However, MI5 are aware of the plot to steal the formula and hot on the crooks' trail. When the absent-minded Professor manages to lose the formula, undercover spies, Jones, the villains and a group of National Service recruits are all thrown into disarray. Can he remember where he wrote it in time?