The platoon's supply of ammunition is used up when engaging a low-flying German plane, and Mainwaring sets up a court of inquiry to determine who should be held responsible. The inquiry descends into farce when the platoon attempts to re-enact the event.

General headquarters determines that Mainwaring has never held a commission, and he is demoted to private. Wilson temporarily leads the platoon while Mainwaring attempts to regain his command.