DI Lewis and DS Hathaway investigate the death of an Oxford theology student, Amy Katz, who is found bludgeoned in the courtyard of her college, just below her bedroom window. The attractive young woman was part of a one week clinical study on the use of a new ketamine-based drug as an antidepressant. Dr. Alex Gansa is in charge of the study and he doesn't believe the drug could have contributed to her death. The police learn that Amy Katz wasn't just a random choice for the study but was actually one of Gansa's patients. They also learn that Adam Douglas, another participant in the clinical study, had a history of threatening behavior towards her. When a second one of the clinical study group dies, soon followed by a serious accident involving someone else associated with the case, Lewis and Hathaway are starting to run out of suspects. Meanwhile, Hatthaway sees Dr. Laura Hobson having dinner in a restaurant with a man which leads to an uncomfortable situation between Hobson and Lewis.
—garykmcd