When the platoon is challenged to a cricket match by the ARP wardens, Mainwaring appoints himself captain and gives the standard inept lecture. They can only hope to make up, in effort, what they presumably lack in everything else, even uniform dress. Hodges, however, signs up as 'warden' — his secret weapon: star player Ernie C. Egan. The vicar and his unsympathetic verger prove unexperienced umpires. Oblivious of most men's obvious physical limitations, Mainwaring's 'brave' approach runs into a record disaster score. However, when Ernie strains his arm, the wardens are a man down and the score starts equaling up.

Mainwaring is determined that his platoon should earn the full quota of a dozen stars in a wacky test weekend. Captain Ramsey is in charge and increases the psychological pressure. The intel Wilson hears from another platoon works against them.

The platoon gets its turn at weekend training, for a bomb course. Captain Square convinces Mainwaring that officers shouldn't sleep with the OR (other ranks) so he puts up blankets for him and Wilson, just after he forbade the others to voluntarily 'spoil him'. Next, Square insists a captain can't join his men for beer, rationed to two pints for safety, which the men, especially Frazer, take for disloyalty. In Officer's Mess, Mainwaring naively volunteers to be 'made a cardinal', a rather cruel drinking game.

At a business community function, where both Wilson and Walker outshine him, Mainwaring accepts a challenge to prove his men are a match for the Home Guard's new, regularly trained, physically superior commandos. Their display of 'brains over brawn' should eliminate the commandos-guarded fuel depot by getting a fake bomb there.

When Mainwaring tries to help Jones with his fiduciary issues, the trail is discovered to lead through the platoon, on to Mavis Pike, and ends with Hodges.

Mainwaring is extremely annoyed that the platoon – sans Godfrey, who was too slow – have used up all their ammunition firing in vain at a low-flying German aeroplane. An inquiry is ordered – along with a new case of ammunition, which duly arrives. The captain in charge, taking place in the church hall in competition with choir practice, feels it a waste of time but talks the men through what happened.

Entrusted with £500 by local shopkeepers, Jones brings it to the bank only to find a pound of sausages instead. Frazer hypnotises him into recalling when he last saw the money, apparently stuffing a chicken for Mr Bluett, but there's no money in the chicken.

Walker has found a discarded parachute which he cuts up to make ladies' knickers. This leads to an embarrassing examination of the ladies' pants to determine their colour as British parachutes are white and Germans are cream. Using a tracker dog, the platoon go into the woods where they trap a man with a foreign accent – but he is an Austrian birdwatcher hunting the rare golden oriole.

Mainwaring has visions of promotion for himself and Wilson, and of expanding the platoon into a company, so he embarks on a recruitment drive. A poster is drawn up and Jones is voted to be on it. Unfortunately, a mix-up at the printer's results in Jones being branded an escaped POW instead.

As all the road signs have been removed, the platoon are ordered to put up temporary ones to help a large convoy on manoeuvres due to drive through the area. However, due to the condition of the ground, Jones's van gets stuck in the mud.

At the bank, Mainwaring's office door is replaced with one made of paper. Adding insult to injury of not having a proper entryway, Mainwaring is more annoyed at Pike, the Colonel, and Jones destroying it within minutes of installation. Meanwhile, Godfrey's cottage is due for demolishment to make way for a new airfield but no one can bring themselves to break the news until Jones finds out that he already knows.

Mainwaring is furious to learn that Wilson is leaving to become manager of the Eastgate branch, where HQ has also appointed him platoon commander with a promotion to Second Lieutenant. While everyone else is congratulatory, Mainwaring's jealous, socially inferior superior implies it's just the old boys network. He promotes Pike to chief clerk, and orders him to copy for all platoon members a promotion to sergeant, meant only for Jones, but so phrased each thinks to get three stripes, creating a Mexican army assembly.

Godfrey reveals that he was a Conscientious Objector during WWI, leading Mainwaring and some of the platoon to brand him as a coward. However, during an exercise in which Mainwaring collapses with smoke inhalation, it is Godfrey who, at risk to himself, rescues him.

The platoon are on guard duty on a derelict pier, which they have reached by boat but, thanks to Pike's clumsiness, the boat has floated away, carrying their food. Hodges rows out in a children's boat to tell them to 'put that light out' and falls into the sea. Dispensary chocolate turns out to be a cardboard display but worse is to come when a floating mine appears.

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 Guard of Honour. 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.

The Colonel orders the platoon to make a training film with a couple of well-known actors, but unknown to Mainwaring, they're to play the Germans. Although Mainwaring refuses to participate, the rest of the platoon is still ordered to do so. When filming is cancelled, Mainwaring and the men, still dressed as German soldiers, are spotted in the local pub and the alarm is raised.

The War Office plans a review of both the Home Guard and the ARP in order to decide which less fit soldiers of the first and less fit of the second should be transferred. As this is the last thing that either group wants, various tricks go towards making them look younger or older.

Elderly ex-soldier Clarke joins the platoon and, by coincidence, it turns out that he and Jones were in the same regiment in 1890s Sudan. However, he paints a picture of a cowardly Jones who left him to his fate when he was captured by Dervishes, and soon after Jones receives two feathers, signifying cowardice, through the post. Jones then tells his story where all the participants look like members of the present; he and Clarke were indeed captured but he rescued Clarke and kept quiet about his affair with the colonel's wife. Mainwaring is satisfied with Jones's account but before he can confront Clarke, Clarke departs.

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.

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.

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

Mainwaring fears the Nazis may send spies across the Channel, so he orders the lighthouse manned by Jones, Pike, Godfrey and Frazer, who tells a terrifying story. The trio accidentally start the mechanism and are unable to shut it down, their attempts only make it worse until the mighty headlight points to town and the siren blows. On shore, the ARP goes berserk, especially when a Luftwaffe attack approaches, while Mainwaring, Wilson and Walker desperately try to find out how to get to their party without a boat or telephone line.

Whilst Mainwaring is in hospital, Wilson is in charge. Following Walker's speedy departure back to London, leaving only a note behind, Wilson decides to make up the platoon's numbers by allowing the vicar and the verger to join.

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

On the way home after an unpatriotic night at the cinema, Mainwaring comes to the assistance of a clippie being accosted by Hodges. In his dreams, Mainwaring is Napoleon with the clippie as Josephine.

A bomb hits the gasworks where Godfrey and Walker are on duty and the platoon and Hodges go to rescue them from a small room in which Godfrey is asleep. Jones, in an outer chamber, slams the door, bringing the roof down and everyone except Jones is in the small room, which is rapidly filling with water.

Frazer, whom the town has been under the impression has meagre earnings, is, as a matter of fact, rather wealthy. Doctor McCeavedy alerts Mainwaring, who alerts Jones and very soon Frazer's fortune is the subject of town gossip.

The War Office tests an experimental invention for delivering explosives. For secrecy, the test is done on the coast, using three local platoons. Mainwaring's vanity is weaponised to make him blindly volunteer for 'special duties', which turn out to be dirty work.

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

Rumours abound when Wilson is seen with an attractive young woman in a WREN's uniform, causing an argument between himself and Mainwaring who catches him sleeping off a hangover in the church hall. Suddenly, pigeons appear — Walker got them to sell to Jones in the absence of other meat but he has yet to kill them.

After another of Mainwaring's long, creative, 'vital' lectures, Frazer is voted the unfortunate duty of complainant representative for the platoon. Mainwaring tries a suggestion from the manual: the troublemaker is to have a go at being an officer. 'Captain' James Frazer proves an even worse tyrant, as he demotes and promotes but impresses the new area commander, fellow Scotsman Major General Menzies.

During a Wings for Victory fundraiser, the platoon reenact the battle between St George and the Dragon, but friction starts when Hodges and the wardens plan the same thing.

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.

After Mainwaring complains of sloppy slauting, a runaway barrage balloon appears with the Verger clinging onto it. He's rescued and various people, including Godfrey's sister Cissie, are asked to hang on until Mainwaring takes charge. Unfortunately, it takes off in the breeze with Mainwaring on the other end of its rope, dragging him through trees and a haystack until it stops on a railway bridge. The men are about to secure it but then an officer comes by and, in order to perfect the saluting so beloved of Mainwaring, they have to let go of the balloon.

During weapons inspection, Mainwaring scolds Frazer for losing a single spring, rendering the Lewis gun useless, and HQ has no spare parts, so even a court-martial may follow. Frazer believes a coffin has been delivered to the funeral parlour, where the men discover it's at Mr Bluett's surviving brother's home. The hilarious treasure hunt continues even after the burial.

Pike gets his head caught in the park railings and the platoon is summoned to help. Meanwhile, a large bomb has exploded nearby and puts out the gas and water. When Mainwaring returns from out of town, he puts everyone under martial law.

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.

The platoon are on an exercise whereby everyone—except for Godfrey and Jones—ends up in a deserted barn. Jones sees from the map that they have been given the wrong reference and the barn will be blown up as part of a live ammunition demo.

The platoon are on night watch in a beach hut, waiting for Pike to bring their tea but Pike has got himself tangled up on barbed wire in the middle of a minefield. Waiting for an engineer to free him, Mainwaring and Frazer mount a rescue attempt of their own, beaten to it by Godfrey. Pike is freed and when the engineer turns up he tells everyone that Pike was never in danger because the minefield was some two hundred yards further along the beach – though Jones knows better!

Mainwaring is to umpire in a war game exercise so he gets the use of a car. Pike meets a girl and uses the car to take her out, but they stay out all night, leaving the whole town scandalised.

A parade is organised through Walmington-on-Sea to commemorate Spitfire Week and, after watching a newsreel, the platoon decide it would be splendid to have a mascot. Sponge farms sheep and the men try to catch his ram but it eludes them every time. Walker provides a goat, a skinny, pitiful creature which eats Mainwaring's £5 note. Down a mascot, the platoon, Hodges and his wardens, the verger and his Sea Scouts, and the volunteer nurses all march faster and faster to be at the head of the procession until the parade becomes a marathon.

The platoon is called to seize a German pilot whose parachute is caught on the church steeple clock. Getting him down is hard enough, given the language barrier. Then Jones manages to drop the ladder and the warden refuses to help.

Mainwaring's lecture is a total mess due to gas masks. To obtain rationed petrol, Joe convinces Jones to volunteer his butcher's van as platoon car. Alas, after they worked for days to make it fit for the platoon, HQ has it converted to gas. Meanwhile, to Mainwaring's snobbish horror, vulgar grocer Hodges makes his haughty entry as ARP Chief Warden, and rival rooster in town and church hall.

Square ridicules Mainwaring for the pitiful state of his men's rifles. The captain rudely denies it but internally blames Wilson's lax inspection techniques and overall poor style. Worse is to come when the ARP have Mainwaring formally charged for an unobscured light emanating from the church where his platoon is.

A large field gun has been delivered for demonstration but none of the platoon know how it works. After a process of trial and error using models to represent the town, the time comes for the gun to be fired but the men get tangled up in the netting enclosing it.

On return from London, Mainwaring is shocked to find that almost all of the platoon are playing in a darts tournament against Hodges and the wardens, which they refuse to leave, despite losing. Wilson is displeased as Hodges has bought Mavis a drink and seems to be getting overly familiar with her. When a call comes through that a suspected IRA terrorist is in the area, however, the men pull together – eventually – and Wilson proves to Mavis and the others that he is the hero of the hour.