Five years after his friend and mentor's death, Lewis - now promoted to position of inspector - returns to the city of Oxford after working on the British Virgin Islands. Even before he has the chance to get home and settle in, he and his new, vastly younger partner DS Hathaway are called to a crime scene to help investigate the murder of an American college student. It is soon discovered that one of the suspects has had past dealings with the late Inspector Morse.
Oswald Cooper is the prime suspect in the rape of a teenage girl, but presents an alibi supported by three pillars of the community. When Cooper is murdered, Lewis discovers a web of deceit going back 20 years, in which the dead man was used by the trio to cover up a sordid series of secrets - but the case soon takes on a personal dimension for the inspector.
After the body of Dr Stephen Black is found on an Oxford tour bus, DI Lewis and DS Hathaway are lead to Crevecoeur Hall, a sprawling Oxford estate where Hathaway spent much of his childhood. Lewis begins to worry that a previous case involving the murder of a ten-year-old girl has begun to affect Hathaway's state of mind, while Hathaway himself seems more interested in the glamorous Scarlett Mortmaigne, the daughter of the owner of Crevecoeur. When another body is discovered on the estate, Hathaway's refusal to believe that the family are involved threatens to tests his relationship with Lewis to breaking point.
When Andrew Crompton, amateur astronomer and Master of Gresham College, is found dead at the foot of the University Observatory stairs, Lewis and Hathaway find that the finger of suspicion points at all the staff - from tutors right down to the head porter and the college scouts. Lewis uncovers a college-wide blackmail plot and is confused by a mysterious astronomical conundrum. Hobson is unexpectedly drawn into the case while rehearsing for a performance with a local orchestra at the college.
Over an August Bank Holiday, an empty Oxford college is the venue for a weekend attended by professional quiz contestants. Lewis and Hathaway are called in when outstanding competitor Ethan Croft is found floating dead in the college fountain. They learn that Croft was an outrageous flirt with a number of secrets, and the pair race to uncover the killer before the gathering breaks up. Meanwhile, Hathaway discovers that Lewis was planning a romantic weekend at Glyndebourne with a mystery date.
On Halloween night, a university friend of pathologist Laura Hobson is found staked through the heart. During their investigation, Lewis and Hathaway are approached by a medium who claims that they are in grave danger. The following day a student is murdered in the house that Hobson shared with her university friends, and a clue at the crime scene leads Lewis and Hathaway to a third victim. As the body count rises Lewis and Hathaway are forced to acknowledge that Hobson might know more about the deaths than she is letting on.
Oxford's last all-female college is holding a reunion party to say goodbye to one of its most popular professors. After a guest is found murdered, Lewis believes the killing is connected to an attack that happened at the same building 10 years ago. He turns to his former DS, Alison McLennan, to help him with the case but it ends up taking a new twist after two more bodies turn up.
A female bishop visiting St Gerard's College is found dead after drinking poisoned wine, and when another two killings occur, both mirroring macabre murders from Jacobean revenge tragedy, it appears the culprit is targeting candidates in the election to become vice-regent. However, when Innocent learns one of the suspects is hiding a dark secret, Lewis and Hathaway realise the motive is much more twisted.
When a student is found dead during a college-based clinical trial for a new anti-depressant, Lewis and Hathaway struggle to determine whether the incident was murder or suicide, and receive little assistance from the institution's evasive psychiatric professor. A second student's death then leads to the revelation that the trial's participants are all operating under the influence of mind-altering drug ketamine, and that the lines between love, obsession and madness have become dangerously blurred.
When botanist Li Nash digs up the body of recently buried English Professor, Murray Hawes, Lewis and Hathaway find themselves involved in an impossible quest. Murray was a man who was possessed with solving the riddle of Lewis Carroll's "The Hunting of the Snark". They soon find out that Murray had a rivalry with his brother, who is a lecturer in Theology and Moral Philosophy. They also have to deal with interference from Michelle Marber who is an amateur detective, who believes that that the killer is local medical researcher Alex Falconer.
Lewis and Hathaway are drawn into a world of virtual bullying, but very real murder, when Professor Miranda Thornton is found dead after her dating video is leaked onto a vicious website. Miranda's death initially looks like suicide but, as the detectives dig deeper, they realise that it is actually the final revenge of an old enemy.
The body of Richard Seager a former Biochemist, is found under a Jaguar Mark 2. The day before, the victim had been collected from prison by his wife, Martha Seager after serving a year for causing death by dangerous driving. Before his death, Seager managed to scratch the number ‘500’ into the car’s paintwork.
Lewis, Hathaway and Hobson look around the new crime scene as Carl Drew, Stella Drew, Martha Seager, Adam Tibbit, Graham Yardley and Adam’s girlfriend Rachel Cliff wait anxiously. The body is revealed to be that of Soo-Min Chong, a Korean student who vanished 15 years ago. Seager was the last person to see her alive, Carl Drew was her boyfriend, and she was Martha’s organ scholar at the chapel. Hathaway is later shocked to discover Adam’s body at the school, with a simple suicide note. Carl, Adam’s former teacher believes that he must have pushed the boy too hard. Forensics end up revealing a close relative of Adam’s had been in Seager’s car. After Martha is found stabbed to death, Lewis and Hathaway start to close in on the killer who is becoming more desperate to cover their tracks.
After a difficult start, Lewis and Hathaway's partnership seems to have gained some semblance of normality. DS Maddox has become a part of the team. Her abilities will be put to the test when an investigation begins on the brutal murder of an American classics student Rose Anderson Her body is hauled from the canal with a stand wound to the neck and abdomen. Suspicious soon fall on astrophysics professor, Felix Garwood who had recently broken off an affair with Rose. However, Felix was married to Rose's supervisor, Philippa Garwood. Could the jealous wife have committed such a murder?
Faced with the seemingly impossible task of identifying the remains of a body discovered in a well, Lewis has also got to contend with new boss Chief Superintendent Moody. Realising that the body in the well is connected to the murder of young artist Talika Desai, the police follow leads into the worlds of drugs, social media and the homeless community, but will they manage to link all the pieces together?
Lewis and Hathaway are called to investigate a body in some woodland. But realising three more murders are to follow, the team must hurry to catch the killer, before they happen. Hathaway is struggling to cope with his father’s illness, as he begins his search to find out who he was before the dementia kicked in.