When a flu epidemic reduces staff numbers at the local police station, three trainees are drafted in. Sergeant Frank Wilkins assumes responsibility for the recruits, but Inspector Mills warns him that he may face transfer to another station.

The three recruits - playboy Tom Potter, superstitious Charlie Constable and pompous Stanley Benson - look for the police station. Potter unwittingly asks directions of a jewel thief, who has just completed a robbery. Sergeant Wilkins inspects the recruits on arrival. A phone call to the station reveals how Potter accidentally aided the jewel thief.

Special Constable Timothy Gorse, an extra recruit, arrives carrying a budgie. Policewoman Harrison leads the four trainees to their quarters in the cells, where Potter flirts with Harrison.

On patrol, Gorse discovers a child's scooter, which he rides, colliding with Benson, who is walking a police dog. WPC Gloria Passworthy reports to Sergeant Laura Moon for temporary attachment. Passworthy has arrested a local drunk, Mrs May, for disorderly behaviour. She escorts Mrs May to the cells, where she meets the new recruits. Passworthy informs them she has replaced Harrison due to the flu. Charlie Constable tells Potter he thinks Passworthy is beautiful.

Benson explains to Gorse that he can tell whether a man is a criminal by looking at his face. Soon after, an honest-looking man steals Benson's braces, causing his trousers to fall down.

The next morning Inspector Mills surveys the recruits, recognising Potter as a society playboy. Mills indicates to Wilkins that he expects no trouble. Wilkins takes the parade on patrol, but a society girlfriend of Potter's interrupts proceedings.

On the beat, Benson questions a CID Detective Sergeant, mistaking him for a suspected criminal. Charlie Constable, believing he has overheard an attempted murder, breaks into a flat, but discovers only a scantily-clad woman listening to the radio. Wilkins, making sure to keep an eye on the recruits, arrives soon after. He asks the lady if she wishes to make a complaint, but she declines.

Wilkins scolds Benson for ushering an old lady across the road against her will. Potter hears suspicious noises upstairs at a house in Nathaniel Road, while investigating reports of an intruder. In the bathroom, he discovers a semi-naked girl, who has returned home after a lovers' tiff. Potter offers consoling advice. Wilkins, believing Potter is in danger, bursts in just as Potter and the girl are about to kiss.

Gorse traps himself in a church tower while rescuing a cat. Inspector Mills accuses Wilkins of not keeping the recruits in order. But when Mills asks Potter to perform secretarial duties, Potter accidentally burns his papers, then throws a bucket of water over Wilkins.

Potter takes the police dog for a walk, but loses control, knocking Inspector Mills into his garden pond. Mills catches cold and declares that the recruits may no longer patrol unaccompanied.

Questioned by Sergeant Moon, Constable confesses to being in love with Passworthy, but demands to know if she is a Virgo, which Moon confirms. Constable declares his love for Passworthy while patrolling together on the beat. Unfortunately, Passworthy takes a different path to Constable at the moment of truth, so misses his declaration of love.

Benson and Gorse, acting against orders, search for shoplifters in a department store by posing as two old ladies. They attempt to arrest a woman seen placing a girdle in her bag, but discover she is the borough's Lady Mayoress, with a store account. The disguised recruits are forced to flee when a store employee accuses them of shoplifting.

Potter and Wilkins stumble upon a wages robbery, but the thieves escape with £100,000. Inspector Mills tells Wilkins he will be transferred.

Benson and Potter discover the thieves' car. With the help of Gorse and Constable, they locate the criminals in an abandoned house. After a struggle, the crooks are arrested and the money recovered.

Constable overcomes his superstitions when he discovers Passworthy is not in fact a Virgo, but decides he still loves her anyway. Inspector Mills is rewarded with a transfer to the area training college, for inspiring the recruits. Wilkins is promoted to Inspector of the police station. Wilkins and Sergeant Moon kiss.