An unannounced bank inspector from head office is far from impressed by Mainwaring's bumbling while handling some minor cash deposit and black market matters with Jones and Walker. He gets really angry about the way military HG considerations seem systematically to supersede bank interests. After an air raid alarm, an unexploded Nazi bomb is 'found' in the basement strong room and nearly made to explode by Mainwaring and Arthur. Bomb squad captain Rogers takes charge, but while he gets help, the men can't resist 'helping' themselves.