Several skeletons are discovered in a tunnel during a canal restoration project near Midsomer Worthy. DCI Barnaby begins his investigations and discovers that one skeleton has modern dental work. Meanwhile, DS Troy has been promoted to Inspector. He begins his last case in Midsomer, investigating the murder of a teenager, Simon Mayfield (played by Henry Cavill), who had been shot with a gun that he and his friends had been using the previous night. The two detectives discover their cases are linked, and uncover a web of lies, affairs, and domestic arguments alongside a mysterious recluse with a hidden past.

DS Dan Scott arrives in Midsomer as DS Troy's replacement. He is instantly involved in a case in the village of Midsomer Mallow, when a college secretary is found murdered. Soon after a retired doctor is also murdered during the village's annual garden open day. Barnaby and Scott investigate the connection between the two victims, and the murder of a homeless drunk give them the clue they need. Meanwhile, Cully organizes a reunion with a group of old school friends, with unexpected results.

Retired music teacher Arthur Leggott is murdered after disturbing an intruder at his home in Badger's Drift. It is discovered that a musical manuscript by the late composer Joan Alder has since gone missing before being sent to auction. When the manuscript shows signs that it has been written by another hand, a handwritten letter by Joan Alder turns up indicating the manuscript is a forgery. Where the manuscript goes more murders follow.

Peter and Caroline Cave are house-hunting in Midsomer Newton and view a tumbledown cottage in secluded woodland. The following morning they are both found dead in their car near the house. DCI Barnaby and Acting DC Ben Jones enter a world where crooked estate agents, property developers, and eccentric villagers all seem to be withholding information. It is not long before another villager is murdered. The detectives find out that a years-old armed robbery holds the key to the case.

Annie Woodrow is being tried for the murder of her friend Frances Trevelyan. The prosecution alleges that her motive was her love for Frances' husband John. As Annie's trial begins, DCI Barnaby becomes increasingly doubtful of the damning evidence he provided to build the case against her. A chance remark by Frances's youngest daughter and a meeting with an old friend, a clinical psychologist, causes him to re-evaluate the case. With DC Jones awaiting news of his promotion to Detective Sergeant, they find themselves reinvestigating and uncover new evidence that puts the case in a very different light.

The Midsomer Rocks festival is due to take place and music fans descend on neighbouring fields to enjoy the fiesta. The recently reformed band Hired Gun is one of the headline acts, and during their opening performance, the band's vocalist Mimi Clifton is electrocuted on stage. Barnaby and Jones soon discover that other band members could be targets. When another is murdered, they discover that a former member, Ginger Foxton, who disappeared 30 years before and had been presumed dead, could still be alive. The detectives enter the world of rock music to find the killer.

As the preparations are underway for Cully Barnaby's wedding, Ned Fitzroy and Beth Porteous are married in Bledlow village. At the reception at Bledlow Hall, the maid of honour, Marina Fellowes, is found murdered. With the honeymoon postponed, the newlyweds and their guests find themselves under investigation by the police. Evidence soon points to a connection with archery when a fletching is found at the crime scene. Barnaby and Jones uncover a long family history with many secrets, lies, deception, and an illegitimate son. These things become even more complicated when the estate manager and former cook are also found murdered.

In the village of Monks Barton, two couples seemingly disappear from their cottages. When Barnaby and Jones arrive, they learn about the legendary and mysterious haunted woods. Shortly afterwards, a body is found in a shallow grave, giving Barnaby and Jones an accurate description of one of the "missing" persons. The detectives have to delve much deeper into the woods and beyond, to find the answer.

The 'Beast of Midsomer' is blamed when former secret agent Geoffrey Larkin is found murdered in the village of Midsomer Parva with savage wounds to his face. He had been staying at Allenby House, a country manor run by former spies, the Frazer family, as a safe house. Barnaby, who is himself revealed as a former spy, becomes involved in the case. With a break-in at the local museum, a cricket match, rivalries, and secret loves, other murders take place and Barnaby soon suspects the killing of Larkin has links to events in Berlin during the Cold War. After resistance to his involvement from MI6 he finally succeeds in closing the case and bringing the guilty party to justice.

The Midsomer county town has historic connections with the city of Brighton. During a council meeting, Causton Mayor Dave Hicks announces plans for a Chamber of Commerce reunion with its counterpart in Brighton. Barnaby suspects the mayor's proposal to buy coastal land there is fraudulent and reluctantly joins the party. But during their time in Brighton, hated property developer Hugh Dalgleish is beheaded on a ghost train ride. DCI Tom Barnaby teams up with his cousin, DCI John Barnaby of Brighton Police, to investigate who is responsible before other murders take place.

A quiet spa weekend at Swavely Manor proves far from relaxing when Tom and Joyce arrive and a female client is found murdered in the flotation chamber. Barnaby interrupts his spa treatment to investigate with Jones. The mystery deepens when the victim's husband disappears. As Tom worries about his future and health, one of the hotel proprietors is also murdered. When the case is finally solved, Barnaby announces his impending retirement. His successor is announced to be his cousin, John Barnaby, who is a newly appointed DCI at Causton CID.

New Causton DCI John Barnaby arrives in Midsomer county. Years earlier, the body of a renowned racing car driver had been found at the prestigious Darnley Park Girls School, apparently having committed suicide with a revolver. The school is now hosting a vintage car rally, but the event is disrupted by the death of one of the judges, a local celebrity DJ. Initially, his death is also presumed to be suicide, but Barnaby soon spots evidence suggesting that both victims had been murdered.

The lives of elderly eccentrics William and Mary Bingham come under police investigation when a social services inspector is found dead in the river, apparently from a canoeing accident. Barnaby is suspicious and quickly concludes the death was murder. He and Jones investigate a local artist community and the significance of the death of the Binghams' son and daughter, many years previously. The collapse of a tower of newspapers brings a further death. A printed image of the lunar surface provides the clue that enables the detectives to identify the killer.

Lucy Oliver, daughter to friends of George Bullard, disappears from a manor house being used by the Oblong Foundation, a New Age cult organisation. Bullard asks for Barnaby's help in finding out what happened to her. The Oblong Foundation is renting the manor house from Ruth Lambert, who inherited the house from her parents after they were killed in a boat explosion. DS Jones, who has recently returned from an undercover policing course, joins a group of Foundation inductees under an assumed identity. He becomes increasingly uncomfortable when one of the female inductees, along with Ruth herself, seem to be emotionally drawn to him. Meanwhile, Barnaby looks into the death of Ruth's parents, suspecting murder, and believing the events all to be linked. These suspicions seem to be confirmed when one of the Foundation leaders is found stabbed. When the case is finally solved, George Bullard announces his retirement.

Farmer Alex Preston's dead body is found in the centre of the ancient Crowcall stone circle days before the spring equinox. Early evidence points to a community of New Dawn Druids, who had been angered over Preston's plans to plough the meadow and make the sacred place inaccessible. But when one of the druids is also murdered, Barnaby realises that more complex motives are involved, and his suspicions turn in a direction that threatens to create a serious rift between him and Jones. Maps that reveal the location of a hidden Anglo Saxon treasure, along with a more modern valuable painting, provide the clues that lead to a very manipulative killer.

When Eve Lomax, a film journalist writing a book about 1960s horror actress Stella Harris, is found dead in Midsomer Langley, it appears her neck was punctured by a vampire. Shortly afterward, Stella's more famous sister Diana Davenport returns to the village after a 40-year-old family rift. The series of killings continues, each depicting deaths similar to those in Stella's films. Barnaby and Jones finally discover who is behind the crimes.

Midsomer Pastures is on the map due to its famous connection with producing the Midsomer Blue cheese. When Debbie Moffett is lured to the caves and is subsequently bludgeoned by a wheel of cheese, it leads the detectives to investigate both the secret, controversial plans to modernize the dairy and the private lives of the parents of children at the local preparatory school in the same village. During the family dinner, Poppy Ordish, daughter of Beatrix Ordish and Oliver Ordish, refuses to eat beef. When more people are killed, long-held secrets about the dairy, school, and villagers are revealed and play a key role in catching the killer. In the end, John, Sarah, Sykes the dog, Ben, and Kate celebrate the Barnabys' 15th anniversary.

DCI Barnaby, assisted by new DS Nelson, arrives in the village of Morton Shallows to investigate the death of furniture maker and local philanderer Conor Bridgeman during a ghost-hunting party at the local Manor House. The murder victim had been stabbed with an antique sword. The Manor has a haunted reputation involving stories of a blacksmith's daughter, and the voice of a young girl on a tape recording from the night of the murder adds to the mystery. Ross Clymer, landlord of the Blacksmiths Arms pub, has his own version of the ghost story, but also becomes a victim when he is discovered in his walk-in freezer, having been bludgeoned to death with a blacksmith's hammer. The identities and history of many of the characters must be unravelled before the detectives arrive at the truth.

Eric Calder, Chairman and boss of Calder's Biscuits, is found murdered whilst on a business trip in Copenhagen. He had been poisoned with strychnine applied to a box of Calder's biscuits. It is discovered the box had been sent from the village of Badger's Drift, home to Calder's firm. The detectives team up with two female Danish police officers to investigate, where suspects and motives abound before the mystery is unravelled.

The launch of the latest sparkling wine, which is produced by the Carnarvon Estate Winery in Midsomer Vinae, loses all its fizz when wine critic Nadia Simons gives it a very harsh review. Moments later, guests who had been sampling the vintage start collapsing. Owner William Carnarvon suspects the Farmers' Wives' Association of trying to destroy his business. Kate Wilding tells Barnaby and Nelson that the glasses had been laced with slug poison. There are many suspects and motives and the detectives set out to piece the puzzle together.

When wealthy landowner Gregory Lancaster's body goes missing on the night of his death, it starts a series of mysterious events in the village of Little Malton. DCI Barnaby, DS Nelson, and new forensic pathologist Kam Karimore enter a very macabre world of body-snatching. Nothing is quite what it seems, and when another strange event takes place, the detectives set out to catch the culprit.

When the annual harvest fair arrives in the village of Whitcombe Mallet, it reopens old wounds for some villagers. After the son of an equestrian centre owner is found trampled by his own horse, the detectives have to look into a case with much complexity that has its roots in the past, in order to solve an investigation where nothing is what it seems.

The village of Little Auburn, which had been requisitioned by the army in World War II and afterwards abandoned, is to be reopened. There are competing visions among the villagers for its future. Finn Thornberry, who had envisioned an eco-friendly village, is found crushed to death by a tank. DCI Barnaby and new DS Jamie Winter investigate and find suspects among the factions of rival bidders. When Roderick Craven, the head of the judging panel that will decide Little Auburn's redevelopment and his brother Milo are also found murdered, an unexpected new beneficiary of the rights to the village comes to light.

Lower Pampling sees a cricket tournament with a new format that controversially breaks with tradition. When star cricketer Leo Henderson is murdered in the club's training shed, DCI Barnaby and DS Winter eventually find out that this case is about gambling, bribery, burglary, and the disappearance of a local woman. Winter finds it suspicious when the man who found the body, Jack Morris, keeps showing up before him and Barnaby as they investigate. Barnaby is surprised when he sees Morris for the first time. It is former DS Ben Jones, now promoted to DI in Brighton, and working undercover.

At the end of the Thassington classical music festival in the village church, the winner of the Falconer Award is announced as Jacob Wheeler. There are many shocked and disappointed musicians and audience members, who feel that pianist Zak Sowande should have won. When Jacob is found strangled with a violin string and the treasured Stradivarius violin on loan to him disappears, Barnaby and Winter must delve into rivalries, disappointments, and hidden identities.

Adam Asoba is found murdered, having been boiled to death in one of the vats at the newly opened brewery of the famously cursed abbey in Midsomer. Dr. Fleur Perkins, a new pathologist, tells Barnaby and Winter that Adam Asoba was living under a false name, and that he actually died three years earlier, under the name Adam Dumont. Adam’s widower, Kwame Asante, turns up at Adam’s house admitting the truth. It seems that he and Adam had big debts, and the only solution for them was for Adam to fake his death so that Kwame could start a new life by collecting a life insurance. The first murder seems to be the end of it, but when Emani Taylor, the woman responsible for the new brewery, is also murdered, Barnaby and Winter must look deeper to find the killer.

The body of Mahesh Sidana, butterfly collector and founding member of an elite IQ society, is found pinned to a wall in a manner akin to his treasured butterfly specimens. This is the first of a series of strange murders that evoke trapped insects. DCI Barnaby and DS Winter are thrust into a crime that impacts not only their community, but internationally. With the help of an old friend, they set out to catch the culprit before another victim is found.