Charlotte has some freedom now that Moriarty thinks she's dead. She agrees to assist the Crown in tracking down information leaked from a spy by following a governess and her wards on a cruise. On the same ship are her charming co-conspirators Mrs. Watson and Lord Ingram, her unsuspecting sister Lydia, and her despicable mother, Mrs. Holmes. A murder happens on the ship and Charlotte in her disguise and team seek to track down the perpetrator making her mission more suspenseful.