Because of a 'flu epidemic, three police constables straight from college are sent to a local constabulary as temporary replacements: Potter (Leslie Phillips), Benson (Kenneth Williams) and Charlie Constable (Kenneth connor). Joining their ranks is Policewoman Gloria Passworthy (Joan Sims) and Special Constable Timothy Gorse (Charles Hawtrey)

Sergeant Wilkins (Sidney James) is in charge of the quartet and he soon learns that Charlie's life is governed by his belief in astrology; Benson has advanced theories on criminology and Potter always has an eye for a pretty face. In fact the new recruits are a pretty hopeless bunch.

Sergeant Wilkins is ably assisted by Laura Moon (Hattie Jacques), a super-efficient woman sergeant.  While on duty Gorse, helping to find a lady's cat, ends up in the belfry of a church by way of the bell ropes. Charlie, hearing a murder being committed, dashes to the aid of a helpless woman, to find that she has been listening to the radio.  Benson helps a deaf old lady to cross the road but finds that she has already spent ten minutes getting to the side they have just left. Potter is persuaded to investigate footsteps in an apparently unoccupied house and finds Sally (Shirley Eaton) just getting into the bath.

Inspector Mills (Eric Barker) issues orders that the quartet are to be accompanied on duty in future.  Charlie goes on patrol with Gloria Passworthy and proclaims his love for her after finding out that her birthday coincides with his own.  Benson and Gorse defy the Inspector and dress up in women's clothes to act as store detectives. In their enthusiasm, they apprehend the Lady Mayoress of the Borough for stealing a pair of corsets. Meanwhile, Potter has become driver of the police car under Sergeant Wilkins' supervision. On finding an abandoned wages van they givechase to the crooks' speeding car but Potter loses control of the vehicle.

Inspector Mills is disgusted with their efforts.

Whilst on his beat later Potter recognises the crooks' car and with Benson drags Charlie and Gorse off their beats to find the crooks.  After a systematic search and slmost giving up hope they come across the crooks hiding in a derelict house.  A desperate fight ensues but Gorse triumphantly raises his truncheon and knocks each crook out cold.

After this success our heroes learn that Inspector Mills is to be transferred to the Area College in charge of morale and discipline and Sergeant Wilkins is promoted to the rank of Inspector in charge of the station.