When some skeletal remains are found inside a bricked up wall of a canal tunnel, DCI Barnaby takes on the challenge of finding the cause of death for one of them who was killed decades after the others (who presumably died in a cave-in.) Meanwhile DS Troy investigates his last case in the area -- the killings of young men who were known to be harassing a local homeless man -- and dealing with the resentment of his former co-workers now that he has been promoted to Inspector.
A cave in of a local canal tunnel under restoration reveals the skeletons of eight individuals. While most of the skeletons are from a cave in when the canal was under construction in the 19th century, one is obviously of a more recent vintage. Dental records identify him as Eric Edwards who was reported missing in 1965. DCI Barnaby delves into the history of the canal to see if he can find a connection. DS Troy is over the moon when he learns that he has qualified as a Detective Inspector and that there may be a job for him in another county. In what may be his last case in Midsomer, he follows up on an anonymous tip that teenagers are harassing a local hermit, Tom. When one of those teenagers is shot through the head, Barnaby leaves "Inspector" Troy in charge of the case.
- John Nettles as DCI Tom Barnaby
- Daniel Casey as Sergeant Gavin Troy
- Jane Wymark as Joyce Barnaby
- Laura Howard as Cully Barnaby
- Barry Jackson as Dr. George Bullard
- David Bradley as Tom
- John Carlisle as Lord Fitzgibbon
- Tim Woodward as Timothy Webster
- Cherie Lunghi as Lillian Webster
- Marc Buchner as Daniel Webster
- Henry Cavill as Simon Mayfield
- Jamie Thomas King as Steven Curtis (as Jamie King)
- Fred Pearson as Charlie Birkett
- Andrew Dunn as Constable Crabbe
- Terence Beesley as Jerry Curtis
- Nicola King as Eleanor Curtis
- Paul Thornley as Sergeant Gill
- Sally Mates as Helen Cartwright
- This is the last appearance of DS Troy as a main character.