Around Oxford, an attractive young woman, Vicki Walmsley, conducts an interview about religious faith with an unflinchingly devout subject; a psychic, Justine Skinner, turns her Tarot cards; and a young man leaves his wife and baby for a meeting at work. This same young man is soon consulting as a psychic with a grieving woman, communicating with spirits from beyond. His next client, however, exposes him as a fraud. Before long, he is found dead in his swivel chair, his face frozen in a grimace of terror.
Hathaway (ensconced in a neck brace for whiplash sustained in a car accident) arrives on the scene with Lewis. They soon find out that the psychic, Randolph James, is actually Reuben Beatty, a research fellow from the University of Oxford's Department of Psychology. Why an Oxford post-grad devoted to researching religious belief and debunking faith in the afterlife is moonlighting as a clairvoyant is puzzling not just to Lewis and Hathaway, but also to his wife, Polly. But Polly has long suspected Reuben of secrets, particularly romantic ones. She thinks he was having an affair with his colleague, Vicki Walmsley.
While Reuben's pompous mentor, Andrew Crane, is surprised to learn about his double life, Vicki admits that she was involved in creating Reuben's secret life as Randolph James, as part of an elaborate investigation into the psychology of faith, conducted in the "real world" outside the laboratories. But she denies having any romantic link with him. Polly, confiding in her teenaged brother, Joshua, is still suspicious. She finds her husband's hidden appointment book and searches for answers.
Lewis and Hathaway learn that Reuben was given two injections: first, a barbiturate to sedate him, then a powerful paralyzing agent strictly used on large mammals, etorphine, which would shut down the respiratory system in seconds. Hobson explains that, with the use of the pain-free etorphine, the death has all the hallmarks of euthanasia. Lewis and Hathaway look to area vets to see if any of the controlled substance has gone missing, and on Hobson's recommendation, consult with Kanan Dutta, a local advocate for assisted dying who is mourning his late daughter, about assisted death. He is familiar with etorphine, having worked with his wife as a conservationist in Angola and used the drug to sedate elephants.
DNA evidence matches a hair follicle in Reuben/Randolph's office to the Tarot card-reading psychic, Justine Skinner. When questioned, Justine claims to be in touch with Reuben's spirit, which has told her that his murderer was a psychic name Frank McLean. Lewis interviews a very smug and hostile Frank (the client who had exposed "Randolph" as a fraud), who denies the charge. Meanwhile, Vicki shares with Hathaway her suspicions about Professor Crane, who is devising a series of secret experiments for the military. Reuben had gotten wind of the experiments and objected on moral grounds. Could they have had him killed to silence him? She won't say more, as she's frightened for her own safety. For good reason; while jogging, she is assaulted by a hooded runner, and seconds later, dies in Hathaway's arms. Etorphine poisoning.
As Lewis and Hobson examine Vicki's body, a theft of etorphine is reported by the Garsington Equine Centre. The drug was last used a year earlier on a horse that had injured its teenaged rider, Joshua Grace – the brother of Reuben's wife, Polly. Another familiar name is on the list of Garsington volunteers: the psychic, Justine Skinner. But Justine was in custody when Vicki was murdered. The other major suspect, Andrew Crane, also has an alibi for the time of Vicki's death.
Joshua initiates a meeting with Lewis, revealing that his mother had been to Reuben's office the day of the murder. Confronted, she admits to it, but denies murdering her son-in-law; she was simply offering him money to leave her daughter. He had refused, revealing that he was doing the counselling to earn money for a proper home for his family. Polly, consoled by confirmation of her husband's true love, surrenders her husband's appointment book, which reveals an unknown client who went by the initials of 'K.D.' A search of Crane's files reveals that a 'K. Dutta' was once a volunteer at the Department of Psychology. They arrest Dutta, who admits guilt to everything. But Hathaway, discovering that his wife's name is 'Katherine,' suggests that Kanan is covering for her, that _she_ was the one who visited the psychic and volunteered, all in order to reconcile her daughter's death. When she recognized Reuben in his true context, at the lab, she was crushed to realize that he was a fraud; the comfort he'd given her empty and false. What's more, if she is the murderer and is killing off Crane's team, Crane would logically be the next victim.
They intercept Kathrine Dutta just as she is about to inject Crane with a fatal dose of etorphine. Her syringe plunges into Hathaway's neck brace, and the detectives wait in horror to see if Hathaway has been drugged. But the brace absorbed the etorphine! Dutta is arrested. The relieved detectives take some time out to contemplate life, death and the higher powers.