His Lordship's butler Perkins makes Captain Mainwaring lose a shooting bet by telling them to stop target practice while his master is asleep. Captain Mainwaring agrees with the platoon's bitter rival warden Hodges that their contribution to the war effort needs more local respect. He accepts a suggestion to simulate a fifth column attack together. The Colonel at HQ reluctantly allows "Operation Wake-Up" so they all dress up as cutthroats and desperadoes. After being ignored by an active army column and three equally shifty-suited men, their only comfort is that Hodges gets a "knuckle-sandwich" by a burly disgruntled customer (who recognized the entire bumbling lot). However Godfrey, while indisposed in the toilet of vicar's office, overhears Captain Square (Mainwaring's trigger-happy rival) on the telephone believing that the desperadoes are real.

Captain Mainwaring's reservations to accept the 'non-combatant' role of umpire in maneuver exercises (as deputy for the Home Guard colonel) quickly disappear when he learns the job comes with a non-assigned staff car. His platoon might be allowed to keep this car, but he makes the mistake of bragging in advance it would be some sort of limousine, so the less grand model gets him generally laughed at. Next Jones' remarks about military car seating etiquette starts an unmusical dance of chairs in it. Pike's eagerness to be allowed in it as runner and general boyish pride are irresponsibly stirred by warden Hodges's niece Sylvia, a regular army driver and the only girl to look at him in times, who besots him to go to the pictures and makes him take the car, ignoring Jones didn't put the petrol in.

The old rivalry between Mainwaring and Hodges resurfaces as they both organise displays for the local "Wings for Victory" pageant.

Doctor McCeavedy, who signals undertaker Frazer deaths, accidentally discovers his life savings, hundreds of sovereigns, and tells Mainwaring the scrooge should be persuaded to put the fortune in safety. The captain's lecture on money in wartime, after Jones' ludicrous demonstration of fixing bayonets while wearing a gas mask, fails to secure the banker a fat annuity commission, he's even called not trustworthy. However the rumor soon spreads, so after half of Walmington beleaguers Frazer in vain for generosity that never comes, he misses his first parade ever to 'secure' his gold, so they all try to spy where he would bury it at night.

Captain Mainwaring gives a 'top secret lecture on the coastal defense warning system his platoon will guard for a weekend, only to learn even the warden knows. Trouble with Jones' van makes them late to relieve regular troops; they set up camp and have porridge in their bumbling fashion. After a nightly air raid, the vicar comes to say mass. Only then do they see a German bomb, caught in the very wires they guard. Getting it down is a job the GPO turns down, but Mainwaring and other old-timers volunteer themselves, all failing, while wisely reluctant Frank is forced to try more unwise monkey-methods.

At long last Corporal Jones is marrying Mildred Fox. He asks Mainwaring's permission as his commanding officer, which involves the captain being caught over the phone by his wife having coffee with Mrs. Fox and viewing her smalls on the clothes-horse. The nuptials go ahead - with a jam sponge beneath the exotic fake wedding cake - but the platoon are summoned to the promenade where eventually the new Mrs. Jones joins them and everyone drinks a health to the Home Guard.