The HMS Hammersley chases a fleet of boats from which the crew catch fish for live sale to aquarium lovers. Swain works out they must be using greatly diluted poison. Bomber messes up completely, even gets the XO wounded, yet wines about her promotion chances. 2Dads arranges she gets a chance to prove herself 'commanding' him and the XO aboard a boat where poison was found. They get captured and seem pawns between a human captain and his violent rival.