Major Bright (Basil Radford) and Captain Early (Naunton Wayne) become detectives after being thrown out of the army for their failure to capture evil Nazi, Otto Fisch. The detectives are invited to a cricketing weekend by their old chum, Gerald Lawson. Little does Gerald realise that the ball he has purchased for the match contains the famous Rothstein diamond, stolen by Otto Fisch, who will stop at nothing to get it back!