After Dunkirk, coastal town Walmington-on-Sea's banker, Rotarian and alderman George Mainwaring, a commissioned 'veteran' without actual war experience, appoints himself commander of the local defense committee, with his bank staff, chief clerk Arthur Wilson and junior Frank Pike. They enroll town volunteers for the Local Defence Force, although mostly unfit and/or over the 55 age limit and almost no military supplies are available.
The LDV (future Home Guard) is still wanting for military supplies. So Mainwaring can't resists illegally 'requisitioning' anything of use in the Peabody Museum of Historical Army Weapons when it closes for the war. Alas its curator, Lance Corporal Jones' loony, mean 88 year-old father, puts up a crafty, tenacious defence. The loot proves worse then disappointing.
Three weeks later, the L.D.V. still have no military equipment, so they improvised 'weapons' and concentrate on the intricacies of unarmed combat. Mainwaring faces a dilemma when estate squire Colonel Square, a Great war veteran, offers the platoon twenty rifles, provided he gets command. Unfortunately his idea of 'modern' warfare is converting them into cavalry, mounting circus horses he minds. The actual arms provide more surprises.
The uniforms finally arrive, albeit without buttons, and all other supplies remain a matter of 'improvisation'. Grim HQ inspector Major Regan thus scolds the stuff and the black market even before testing the men. STill, thanks to Wilson's instructions the platoon passes. However, Jones is over age, so he's fired unless he passes an obstacle course within 15 minutes, while nightly tests remain over two hours.
Winston Churchill is to visit Walmington-on-Sea and there is rivalry between Mainwaring's outfit and the Eastgate platoon as to which of them will supply the guard of honour for him. The answer is simple - the unit which wins a shooting contest. Since Mainwaring's men are pretty hopeless salvation seems to lie in Laura La Plaz, a stage sharp-shooter of Walker's acquaintance, who has to be disguised as a man to take part. Fortunately Frazer comes to the platoon's aid, being a crack shot who wins the contest.