I've seen all of the Christie TV series- Poirot, Marple, etc. This episode brings back memories of old Christie stories.
People are brought together for a birthday party and are trapped in a mansion on an island and the boat to the mainland has broken free from the dock, so no egress. And rain is pouring down. Cue creepy music....
Barnaby and Winter are trapped too. They get to share a bedroom where Barnaby washes out his socks and dries them on an old fashioned heater. Winter gets to run after suspects in the rain with bare feet. Barnaby gives him no sympathy, as usual. He has a pattern of chasing suspects and falling into rivers or getting wet.
The only thing I disliked about this episode is the diverse casting of many characters. While I understand the current desire to include as many diverse actors as possible, it strains credulity to believe there would be so many actors in a rural British county. Many of Midsomer's later episodes have this problem. It's great when Bridgerton does it, although not realistic or historically correct, but that show is based in London, where it would be more diverse. When you do a show about quaint British villages in the country, you don't expect to see any non-caucasian citizens or residents.