After listening to a radio broadcast asking for men to form what was to become known as the Home Guard, George Mainwaring, a local bank manager, decides to act and form the platoon of his own accord. He appoints himself as Captain and recruits his chief bank clerk Arthur Wilson as the platoon sergeant as well as enlisting the bank's office boy Frank Pike. Several of the local tradesmen - including James Frazer, a philatelist shopkeeper; retired shop worker Charles Godfrey; Jack Jones the butcher and black market businessman Joe Walker - also volunteer their service for 'King and Country.' And so, The Walmington-on-Sea Home Guard was born.

With the shortage of weapons, Capt. Mainwaring goes to the local museum to see if any of the guns on display can be used by the platoon.

Capt. Mainwaring, worried about the lack of weapons, gets a visit from Col. Square, an old soldier who offers to donate some guns from his collection, providing he can take command of the platoon. Mainwaring agrees until he sees the state of the guns.

Capt. Mainwaring is giving a lecture on recognising enemy agents when he learns that for every Nazi captured there is a reward. Later on Jones and Walker capture two Luftwaffe airmen, although a Polish officer intends to claim the reward. Back at HQ the airmen escape on Godfrey's watch.

Just when the platoon finally gets its uniforms, LCpl. Jones is told that unless he can complete the assault course in 15 minutes he will have to leave, so Mainwaring and the rest of the platoon think of a plan to help him.

When news that the Prime Minister is to pay a visit to the area a shooting contest is held to see which of the local platoons will form the honour guard. Walker gets a crack shot from the theatre touring show (Barbara Windsor) to take part as a member of the platoon but a surprise is in store for everybody.