The Walmington-on-Sea Home Guard is excited to be selected to 'act' in an army film, but when it becomes clear they'll play Nazis and how unkind the camera could be, Captain Mainwaring refuses 'patriotically' to participate; Frank and Arthur are chosen as German officers. The whole 'cast' is to travel in Jones's butchery van on a hot day, only to be told their scenes are delayed. Against orders, they leave in costume for drinks in a bar, where the landlord is convinced they are enemy troops and informs the warden, who passes the panic message on to the police and the local Home Guard headquarters in church, where he finds only vicar and verger, who help him ring the bells as invasion alert.

Despite his mother's advice to get out of service, Pike proudly announces he passed the medical for the real army's recruitment, and he's to become an RAF Airman. Meanwhile Mainwaring is jealous of Hodges's promise to raise 50 pints in the town's blood drive just to get a fancy certificate, so he rashly pledges 100, despite Wilson's warning, but finds the platoon's health and Hodges's promise of onions leave his team at three! At the last minute, Jones and Frazer bring most surprising 'reinforcements'. Now everybody feels they've earned celebrating with the fish and chips 'surprise' party for Frank's departure, but he willingly withheld a surprise result of his blood donation..

Three months after the bomb on the bank, Mr. George Mainwaring makes a terrible fuss about the 'undignified' standard government-issue new door for his office, even before it becomes clear the tar paper is also fragile rubbish, ruined within minutes. Alas an early visitor, the Home Guard Colonel, brings a worse concern: Defense is building a new aerodrome for the RAF, and the idyllic cottage Mr. Godfrey lives in with his sisters Dolly and Cissy must be demolished to make room for it, the platoon is asked to break the news before the official notice. A visit from Mainwaring, Arthur and Pike is most enjoyable, tea and home-made refreshments in the sort of country garden with blooming roses 'just what we are fighting for', but neither has the heart to tell their generous hosts' tiny ancestral paradise is doomed. Now Godfrey's contemporaries are to tell the Nestor, during guard duty, but Frazer only contributes 'Jones had bad news for you'; Godfrey however surprises him - the notice already arrived. Yet Frazer has the biggest surprise, which none of the others is told about, even while they all help the Godfrey family move, because of a deceptive Scottish politician...

In preparation for a bivouac weekend, Captain Mainwaring gives a lecture, in the vicar's garden as the indoor church premises are spoken for, so the gardener bothers the vicar, who prepares his sermon, about the Home Guardsmen behaving 'improperly'. After lessons in hedgehog-cooking in mud - poor Pike - putting up two-man tents without making holes in the lawn - poor Pike, Jones and tent - and starting a fire, actually trying not to light it - poor Pike and lawn - it's off to the field. Alas, Mr. Hodges cheerfully gave a lift to vicar, verger and their troop of Sea Scouts to man a Pirates raft (for the Spitfire fund), running out of petrol so he has to sleep in his van, more undesired neighbors for Mainwaring. The three Nazi crewman of a German bomber - spotted at night by Frazer - have parachuted down into the river, so once they're detected in the morning Hodges, the only one to speak German, is commandeered at the point of Jones's bayonet to join the RAF-commandeered raft for two rather too watery attempts to capture the 'swines' from their inflated dingy.

Captain Mainwaring feels his local bank branch can no longer honor Mr. Jones's checks because his account has a five month overdraft of £50. After hours, the 'financial genius' trio goes through the shambles that passes for his butchery bookkeeping but, only when half of the platoon has assembled in the vicar's office for a 'private' consultation, does Jones pull the problem out of his pocket: he is owed £50 by the orphanage and that's just the last link in a chain of debts and dues, with an extra creditor lurking around when half the village has assembled in church on Mainwaring's orders...

Mainwaring scolds Sergeant Wilson for his 'unmanly general appearance' because HQ is considering to upgrade his platoon to company, which could get them promoted. So he eagerly sets about planning a recruiting campaign to triple their manpower. The men decide on a poster, sausages on the proud 'macho' model: Lance Corporal Jones. As photographer Mr. Bluett is even older, posing proves a delicate business. However the overworked printer does worse, mixing Jones's mugshot up with one for an escaped POW. Mainwaring's arrogant approach to reclaim his man makes things much worse still.

Captain George Mainwaring berates Frank for writing a humorous draft magazine article on the Home Guard, especially because it mentions drinking. Next he 'volunteers' the platoon to host a sherry party for Home guard officers. His haughty attitude is duly dimmed when his brother Barry, a party toys salesman, arrives by train, who reveals their humble roots.

The vicar holds a charity bazaar, the proceeds going to luxuries for the troops. Godfrey tries to sell his home-made wine but people are getting drunk by tasting and not buying it. Mrs. Mainwaring fails to turn up after an accident with the bath enamel but donates some hideous lamp-shades she has made. Hodges contributes three oranges and Mainwaring is anxious to secure one for his wife but when Wilson gets Pike to buy it for the captain, the two end up bidding against each other and raising the price of the orange. Mainwaring finally buys it only to find it is a bitter orange, for marmalade-making.