The codebreakers of Bletchley Park decide to raise money for the town's Spitfire fund to try and get them out of the doghouse. Unfortunately Charles promptly loses the money in a card game, trying to impress an old school chum, so the hut must try to win it back somehow. Archie can't believe Charles is so desperate to curry favour with a former prefect and Minka has trouble understanding the rules of gentlemen's clubs.