When heirs of the aristocratic Smythe-Webster family are killed, Barnaby's investigation uncovers long-hidden family secrets.
Someone is decimating the ancient Smythe-Webster family of Upper Warden, and the bad blood between the villages of Upper and Lower Warden is renewed with a vengeance. First, young heart-throb actor Larry Smith (alias Laurence Smythe-Webster) dies in an explosion at a publicity event for a new film. House of Satan is based on a book by a local writer, the late Ellis Bell of Lower Warden - a village whose inhabitants are referred to by its Vicar, the Reverend Simon Smythe-Webster, as "the weasels of the wild wood". The next to die is Larry's uncle, House of Satan producer Frank Webster (Francis Smythe-Webster), electrocuted to death on his exercise bike. Finally, Barnaby's principal suspect, Danny Pinchel, the family's cook, is drowned in a large bowl of tomato soup... Barnaby realizes he is dealing with an historic grudge, and he inquires into the family's antecedents.
- John Nettles as DCI Tom Barnaby
- Daniel Casey as Sgt. Gavin Troy
- Jane Wymark as Joyce Barnaby
- Barry Jackson as Dr. George Bullard
- Ronald Pickup as Rupert Smythe-Webster
- Beth Goddard as Wendy Smythe-Webster
- Christopher Good as Simon Smythe-Webster
- Phoebe Nicholls as Laura Smythe-Webster
- Jonathan Hyde as Frank Webster
- Leo Bill as Darren
- Jo Stone-Fewings as Danny Pinchel
- Tim Preece as Jack Wilson
- Anne Reid as Sarah Proudie
- Alex Lowe as Phil Harrison
- Charlie Beall as Larry Smith
- Rebecca Johnson as Anne
- Danielle Tilley as Emily
- Katy Murphy as Helen
- Jack Chissick as Murdoch
- Brett Reylander as Policeman (uncredited)
- Tom: "Stop Troy, stop. We go down the hill, Troy"
- Troy: "I thought we were going to Upper Warden."
- Tom: "Yeah, we are. Upper Warden is down the hill; Lower Warden is up the hill."
- Troy: "That doesn't make any sense."
- Tom: "Troy, this is Midsomer!"
- Troy: "Sorry, I forgot"
- — Tom and Troy