Mainwaring responds to the call to set up a Local Defence Volunteers platoon; tries to secure equipment that could see off potential Nazi invaders; and nearly loses command of the platoon.
The platoon defends headquarters in an exercise against members of the Highland Regiment; an invasion alert throws Mainwaring's would-be heroes into a panic; and Sgt Wilson struggles to concentrate on his Home Guard duties when he has a personal problem to contend with.
The platoon boosts its fighting strength by acquiring an armoured car; the men head off for a weekend at a training camp; and an enemy aircraft ditches in a reservoir.
The platoon plumps for a ram as a mascot for a big parade; Jones finds himself cast adrift during an exercise pitting the home-front heroes against their arch-rival Captain Square; and Mainwaring starts a foot-hardening regimen involving lengthy route marches.
A daring bid to rescue Walker and Godfrey from a stricken pumping station ends with the whole platoon trapped and facing the prospect of drowning; the older members of the platoon try to look younger; and Mainwaring dreams he is Napoleon.
Mainwaring seizes the chance to contribute to the war effort by guarding a captured German U-boat crew; the platoon welcomes the first American troops to the area; and Mainwaring is asked to provide a guard of honour for a royal train passing through Walmington-on-Sea.
The platoon are ordered to clear the area for a major army exercise; Walmington-on-Sea's power and communications services are cut off; and an exercise with the regular army goes well, until Mainwaring assumes the role of an enemy agent.
The platoon is selected to appear in an army training film; Pike receives his call-up papers and unexpectedly passes his medical; and learns his cottage is scheduled for demolition to make way for a new airstrip.
Mainwaring's men pose as traitors to see how the residents of Walmington-on-Sea would deal with genuine Nazi infiltrators; Pike and his new girlfriend get stranded in the middle of nowhere; and the platoon re-enacts the battle between St George and the dragon.