After hearing of the formation of the Home Guard,George Mainwaring, a bank manager, takes it upon himself to form a platoon in Walmington-on-Sea. He declares himself captain and names his chief clerk Arthur Wilson, sergeant.
Mainwaring, worried that the Nazis could attack at any time, attempts to requisition much-needed weapons from the local Peabody Museum of Historic Army Weapons.
In exchange for weapons, Mainwaring hands over command to Captain Square, but the weapons are muskets and Square wants the platoon to fight on horseback.
Lance Corporal Jones and Private Walker capture two Luftwaffe airmen, earning a monetary reward; however, a Polish officer wishes to claim the reward for himself.
Major Regan from area headquarters decides that Jones is too old to be in the Home Guard, and announces that unless Jones can complete the assault course in fifteen minutes, he will be removed from the platoon.
The platoon is chosen to provide the guard of honour for the Prime Minister on his visit to Walmington-on-Sea, but poor performance at the shooting range causes Major Regan to have them compete with the neighbouring Eastgate platoon for the honour.
