It's Humphrey's last day as detective inspector, but there's no time to dwell, as the whole team is eagerly awaiting the town's annual pirate festival. Danger, however, is ahoy when Geraldine Desai's nautical exhibition goes up in smoke, leading to the ancient treasure map of pirate Elias Cutler going missing amid the chaos. On the trail of the missing map, Humphrey soon has suspicions when he discovers that Geraldine has been selling her memorabilia to pay for her husband's care and recently had the map revalued. Touching base with an antiques dealer, who is adamant the map is worth nothing, the team begin to question if they're dealing with a harmless prank, an insurance job, or something more sinister.
Meanwhile, Humphrey frets about a potential leaving party as Mr Smith prepares to take over. Smelling a rat, Anne recruits Martha and Kelby to launch an investigation of her own. Elsewhere, Esther braces herself to say goodbye to her daughter, unaware that Zoe has prepared a shock surprise.
