An exclusive couples retreat turns deadly when the therapist is drowned at sea during her evening swim. When fingermarks are found on the victim's neck, Mervin confirms foul play was involved, and suspicion soon shifts to her clients - two couples who have paid a small fortune to mend their fractured marriages. But all four were having dinner together at the time of the murder, and while each member of the party slipped away from the table for a few minutes, there's no way any of them could have drowned their therapist in the middle of the ocean and made it back in time... is there?

Meanwhile, Mervin is determined to track down his brother, along with the possessions Solomon stole from him. But Mervin gets more than he bargained for when Solomon's attempts to make amends land them in hot water. Is it the end of the road for these belligerent brothers?

The team are called to St Vincent's, a local church. Sylvie Godwin, an elderly parishioner, has perished after the large cross she was dusting apparently toppled on top of her. It looks like a tragic accident. The church was locked from the inside. And who could possibly want to kill the sweet and pious Mrs Godwin? But Mervin has his suspicions...

The case has a particular resonance for Seb. His mother is the long-time pastor at St Vincent's, and he has grown up in this church. Could one of the congregants, whom he has known all his life, really be capable of murder? As the investigation deepens and secrets surface, Seb must battle to keep his emotions out of a highly personal case.

Meanwhile, Mervin redoubles his efforts to settle into life on the island. After finding himself out of his depth at the local dominoes club, he devises a plan to bring a little flavour of London to Saint Marie.