Blackadder pretends that he's insane to avoid certain death carrying out the General's order for the "big push".
After years of futile trench warfare, General Melchett gives the order for the "big push": a suicidal charge across the battlefield towards hundreds of German machine guns. Desperate to avoid participating, Captain Blackadder hatches a plan to convince his superiors that he has gone insane and therefore cannot go into combat.—Murray Chapman