After listening to a radio broadcast asking for men to form what has been named Local Defence Volunteers (later to be renamed 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 LDV is 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.

When six members of the Highland Regiment attack the Warmington-on-Sea's HQ, the platoon has to come up with a scheme to capture the attackers.

When the church bells start to ring, the platoon leaps into action. Jones takes half the platoon to Godfrey's cottage to set up a machine gun post while Wilson, not knowing where Jones has gone, also heads for the cottage where they both mistake each other for the enemy and prepare to attack.

Walker is finally called up but Mainwaring tries to get his call-up deferred because of his value to the platoon, but he is still conscripted, only to find out that he is allergic to the army's corned beef.

Sgt. Wilson overhears Mrs. Pike telling Frank that she is expecting a child. Wilson assumes that she is pregnant and that he is the father, but it turns out that she is looking after an evacuee. Mainwaring advises that Wilson marry her, until she clears up the misunderstanding.

Capt. Mainwaring promotes Frazer to Lance Corporal, thus causing friction between him and Jones. When Frazer starts getting above himself, Mainwaring cancels the promotion.

The platoon is fire watching when the men see a man using a torch. Convinced that they have discovered a spy, they arrest him only to find that they have made a terrible mistake.

Mainwaring watches a film reel at the cinema which shows Winston Churchill inspecting Army troops and their mascot - a ram, of course where Mainwaring's concerned. If another platoon has a mascot, so must his. Sponge volunteers one from his farm but they have to catch it first; something that of course ends in complete disaster with Pike up to his neck in it - literally. Meanwhile the town parade is being organised and of course Mainwaring wants the platoon to lead, but Hodges has other ideas...

During home guard manoeuvres LCpl Jones, disguised as a log and helped by Frazer in a diving suit, floats down the river in order to attack the Eastgate platoon's headquarters.

Capt. Mainwaring decides to harden the platoon's feet by long route marches. When the platoon has had enough the men find a clever way of stopping him.

The platoon has moved to a new HQ's position on the beach. When Pike fails to turn up they find him caught up in the barbed wire at the waters edge. With the tide coming in, Mainwaring and Wilson mount a rescue mission, but someone else gets there first.

The platoon is manning the local lighthouse and accidentally switches on the light and can't find a way to switch it off. During an air raid they must find a way to cover up the glare.

LCpl. Jones goes to a reunion of his old regiment. While he is away an old comrade who fought in the same battle joins the platoon and accuses Jones of cowardice. Upon his return Jones has to tell the real story.

Capt. Mainwaring decides to enlist women to the platoon to assist with the war effort. After initial interviews go rather less than satisfactory, a Mrs. Fiona Grey walks into his office and into his life. Mainwaring is flattered that Fiona not only has similar views to him about the war, but also is complementary about his persona. He finds himself falling in love. Unfortunately the men very quickly realise and start to gossip behind his back and Fiona decides to leave, but can Mainwaring get to the station in time to stop her?

In a cricket match between the platoon and the ARP wardens, Chief Warden Hodges has a secret weapon up his sleeve: he plans to recruit Ernie Egan (played by England's fast bowler Fred Trueman), a professional cricketer. But all does not go as planned.

Sgt. Wilson becomes a manager of his own branch and gets a commission on the same day. But hours later his new branch is destroyed during an air raid. Mainwaring offers him his old job back and his former rank.

When the ARP Headquarters has been destroyed, Hodges and the wardens move into Mainwaring's office and the two of them start arguing over space. Later the chimney catches fire and they have to work together to put the fire out.

While the platoon is at a training camp, Mainwaring gets drunk with the other officers during the night and misses the live grenade training the following morning. Later during the training one of the grenades lands in Jones's van and Mainwaring rides to the rescue.

The platoon finally gets to grips with the enemy when it has to guard some Nazi submariners. But the Germans turn the tables on Mainwaring and try to escape, resulting in Jones ending up with a grenade down his trousers.

The platoon decides to give a party to the visiting American troops. When the Yanks start to get fresh with the platoon's girlfriends, all hell lets loose.