Hiren Lake Legend Murder Case: File 3 - S1-E6
Plot hole: The plan of the killer relies on a couple of pretty strong coincidences, such as the fact that they wouldn't realise their common link (he knows nothing about what happened on the cruise, so he couldn't know that they all wouldn't realise they have met before) and the fact that the boat is discovered at the perfect time for him to commit murder (on someone who wasn't part of the trip, but is willing to join him).