Accident-prone Ship Steward, Ordinary Seaman Blissworth (Kenneth Connor), manages to destroy the blueprints to a top-secret homing torpedo project. Along with his equally inadequate commanding officer, Captain Foster (Eric Barker), their only hope is to get another set bound for London. But when Admiral Sir Humphrey Pettigrew (Noel Purcell) turns up they try to cover up their mistake by presenting him with a set of plans that detail the ship's refrigeration system. When they discover a female naval scientist, Miss Potter (Hattie Jacques), is due to arrive for torpedo testing, Blissworth is forced to dress in drag and impersonate her. Blissworth's dilemma is exacerbated when the Admiral himself needs keeping at bay because of his amorous intentions.