Amy Katz, a beautiful young student, is found dead in a garden outside the Oxford campus building where a drug trial is taking place. Katz is one of an eclectic assortment of participants in a week-long test of a new antidepressant under the guidance of the confident and enigmatic psychiatrist Dr. Alex Gansa. It isn't hard to imagine almost any of the others harming Katz — an obsessed and angry student, a peculiar ex-soldier, two obstinate warehouse workers and a quirky dog walker. Their true feelings for Katz, from sublime devotion to utter hatred, are soon revealed, and Lewis and Hathaway find themselves with a virtual case study in compelling motives.
Inevitably, the Katz investigation also draws attention to the drug trial's charismatic creator, Gansa. He adeptly deflects whatever suspicion comes his way. But it is soon revealed that he has everything to gain from a successful outcome to the drug trial, and when it comes to his dubious past, everything to hide.
When a second participant is found dead, even more scrutiny falls on the antidepressant, ketamine, a horse tranquilizer and party circuit favorite. Are the trial participants being helped by the drug or driven to murder?
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Warning: Contains significant plot spoilers
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Warning: Contains significant plot spoilers
In a psychiatric drug trial gone disastrously wrong, trial subject Amy Katz is found dead beneath her third-floor window at one of Oxford's colleges, an apparent suicide. As usual, police pathologist Dr. Laura Hobson is with the corpse when Lewis arrives, but she is unusually chilly to him, since she assumes Hathaway has told him about seeing her with another man at a restaurant the previous evening. But Lewis is clueless about this infidelity in their budding relationship.
Fortunately, the case is not without clues, one of which is the murder weapon, showing that Amy had her head bashed in. The suspects include the other trial participants: Amy's fellow student Adam, warehouse workers/lovers Jack and Karen, PTSD-suffering ex-soldier Dane, and dog-walker Shauna. Plus the leader of the drug trial, brilliant psychiatrist Dr. Alex Gansa, along with his beautiful wife, Claire, and his research assistant, Bethan.
Jealously tops the list of motives, since Amy attracted every male who knew her, and she could have sparked violence in a rejected suitor or a resentful female rival. The drug trial itself is also suspect, since Gansa not only holds a share of the patent on the drug and stands to make a fortune if it succeeds, but he is a notorious philanderer with his patients, possibly including Amy. He might well have decided that exposure of his affair with her posed a threat to his career.
The pill plot thickens when Adam turns up dead from an overdose of Gansa's drug. Then Claire is left in a coma after a nighttime hit-and-run while she was bicycling to the police station to give new evidence. At the time, Gansa claims he was at Bethan's apartment, asleep on her couch after calming her down from an anxiety attack.
With all signs pointing to Gansa as the mastermind of the mayhem, he hardly helps his case with an arrogant attitude, contempt for the cops, and insulting psychiatric diagnoses for anyone who threatens him.
But one of his diagnoses proves correct. His assistant Bethan does indeed have de Clerambault's syndrome, also known as erotomania, a sexual obsession in which the sufferer believes that another person returns their ardent love. In this case, Bethan is having a delusional relationship with Gansa, which Lewis discovers when he finds Gansa's old clothing in her closet and scraps of his discarded files in her "therapy session" notebooks.
Confronted in her kitchen by Lewis, Bethan slashes him with a knife, injuring his arm before she is carted away, presumably to a facility for the criminally insane. Bethan's instinct is to lash out at anyone who threatens her imagined lover — as she did to Amy, Adam, Claire, and now Lewis.
In another case of closeted romance, Lewis and Laura make up from their misunderstanding. She had been having dinner with an old boyfriend, who is staying that way. And Hathaway was discreet enough never to mention the tryst to Lewis. "Look," he tells his boss, "I hope that you and Dr. Hobson work it out. Whatever it is, which you've got to admit, is a bit of a mystery."