Barnaby accompanies Joyce to Swaveley Manor health spa, run by fussy Luke Archbold and his wife Phoebe. Luke is in a right of way dispute with Phoebe's former best friend, Miranda Bedford, who has written a novel, and her volatile handyman Carter Smith. Demanding guest Kitty Pottinger is found drowned in the flotation chamber and soon afterwards Luke is killed by a faulty weights machine. The spa faces closure and evidence points to Carter having killed Luke, though Barnaby believes he was framed. Kitty's husband Kenny disappears but is found, having survived an attempt on his life. Before Barnaby retires, handing over to his cousin John Barnaby, he has exposed a fake medium and discovered that the killer had dual motives - hatred for the Pottingers and a need to stop Miranda 's book being published - both instances being fit for murder.
This is the final episode featuring DCI Tom Barnaby and focuses on more personal features of the character. Throughout the episode we are shown an aspect of Tom's background that hasn't been featured before - the death of his father. We find out that Tom's father died on his birthday due to a massive stroke, Tom and his father had feuded shortly before his death and he says that his last words to his father were "not very nice". As such - he deeply regrets his fathers death and ever since has harboured anxiety that he, too, would die at the same age as his father. As that age draws near Tom becomes more pensive and contemplative about his future.
At the end of the episode, having solved the murders, he celebrates his birthday with family and friends and announces his retirement. He and Joyce go on to spend his retirement travelling the world.