Police arrive at the hall looking for Simon. They eventually find him in the priest's hole with his hands tied and duct tape over his mouth. Simon grabs a knife and puts it to Barnaby's throat. Barnaby talks him down. Barnaby asks Simon if he saw who put him in the priest's hole. DCI John Barnaby and DS Ben Jones go to the morgue. Pathologist, Dr. Kate Wilding says "He died around midnight. Cause of death.." Jones inserts, "Long fall, landing on head." Kate says, "How very scientific." Jones says, "It's self-evident. He tells Barnaby that the man fell from the roof of Quitewell Hall. The only witness, Toby DeQuetteville, said he saw a grey horse riding away just after the old man fell. Barnaby says, "And who was out riding in the middle of the night? In a very aggressive electrical storm." Jones says, "Don't know, sir. But apparently, he had no head." (Kate bangs metal tray ) Barnaby says, "I beg your pardon?" Jones says, "Witness said the horserider had no head." Barnaby, "Drunk or stoned?" Jones, "I was on duty, sir." He is Bentham DeQuetteville, brother of Sir Ludovic DeQuetteville of Quitewell Hall. Elsewhere on the estate, Toby is working to straighten out the tire on the wagon. Julian stomps up and tells Toby that the police are there and want to talk to everyone. He tells Toby to "Keep your trap shut about the family business, all right?" Toby says, "What family business?" Julian leans over and pats Toby on the cheek and says, "Exactly. And leave the idiot here," referring to Simon. DCI Barnaby and DS Jones investigate the death of Bentham DeQuetteville, who fell from the roof of the family manor house after seeing a headless horseman in the courtyard. His last word to his nephew Toby DeQuetteville - who also saw the headless horseman - was simply 'Geoffrey'. Several members of the family are quite open about their dislike of the dead man but are less open about the family legend that says the headless horseman is their 17th century ancestor, Geoffrey DeQuetteville, whose appearance always portends a death in the family. Toby's mentally disturbed son Simon DeQuetteville has always claimed that the headless horseman had appeared prior to his mother's death. The DeQuettevilles have had a centuries old row with their neighbors, the Fleetwoods, but two other members of the DeQuetteville family will die before Barnaby figures out just what is going on.

At Quitewell Hall, Ludo tells Barnaby that he saw the headless horseman last night. Ludo says, "It's the ghost of Geoffrey. I'm a goner!" Barnaby says, "Sir Ludovic, if his horse was real, there's a good chance the rider was real too." Ludo says, "No, no, it's Geoffrey. And he's coming for me!" Barnaby tells him to stay inside today with the battle on. Written by one of MM's better scriptwriters, Michael Aitkins, "The Dark Rider," the opening of the 15th season, concerns a yearly re- enactment battle. As the DeQuetteville family readies itself for the Civil war battle, Bentham De Qutteville falls from a roof after he spots a headless horseman. This follows the family legend that states this will happen during a Civil War reenactment. The headless horseman is the ghost of Sir Geoffrey De Quetteville, and his appearance means death to anyone who see him. Then Toby De Q's twin brother dies after seeing the horseman.On the grounds of Quitewell hall, workers are putting up a sound system and testing out the cannon. Up on the hill nearby, at a modern style home, Harry Fleetwood watches Quitewell Hall scratches his arms. Sasha Fleetwood brings him a pill. Harry says, "Every damn year, every damn month they do something. Deliberately corrupt history. I've got to do something. It was Naseby. They never got over Naseby. Diana says to Izzy, "So we've lost Long Meadow as well." Izzy says, "No. Harry just phoned. Says he won't be calling in the debt. Obviously stood up for himself at last. He's a decent man." Diana says, "He's not. Not at all. He's pathetic." Izzy replies, "Diana. Try not to be such a despicable tart. My son was barely cold before you were over the wall like an alley cat on heat. Why do we imagine our domestic staff are all blind and deaf? They aren't. They have big ears. And bigger mouths. It's all over the village." Diana says, "I was trying to save Long Meadow." Izzy says, "You were trying to save yourself from the penury that is about to consume you. And serve you right." Diana leaves and Izzy talks to Ludo's photo. "Don't you worry. We're the king's men. We'll show them."

The next morning, Diana arrives at the Fleetwood house. She flirts with Harry. Diana says that the re-enactment is going ahead. She tells Harry she could bring him a lot more than Long Meadow. She says, "What if you owned both estates?" Harry says, "And how would I achieve that?" Diana says, "The usual way. Marriage. To the right... person." Ludo tells Izzy he is staying inside the hall and skipping the battle. In the meadow, the reenactors are preparing for the battle. Izzy gives a speech to the Cavaliers. Up at the Treadwell home, Harry is nervous due to the cannons blasting. A group of men come marching in, dressed in costume with guns and flags. Horns are blowing. Inside the dining room, Ludo sees a shadow above.Season 15 Episode 1 of Midsomer Murders resulted in a 0.00 rating in the 18-49 demographic. Midsomer Murders Season 15 Episodes...