The police may have a serial killer on their hands when they locate a second body in a site where the first victim was found several months before. The body was trussed up in the same way and had an identical burn mark on his back. There is no apparent link between the first victim, student Michael Haughty, and the second Jason Villers, a probationer at the police college. While the police find evidence that may solve the Otty case, they have nothing on the Villers murder. In a separate case, Harry is approached by the wife of an old university friend who asks him to perform a post-mortem on her husband who died in a fall. Harry finds that his old friend was injecting himself regularly. Leo's family is visiting for a few days but he's constantly being called into work.

Stephen Harrington, a friend of Leo, is concerned that his daughter Rachel, an aid worker, has gone missing in Zambia. Leo and his colleagues fly to Africa where Rachel's corpse is discovered. It seems that she was investigating the deaths of local villagers and may have been silenced. In the absence of the local coroner, the team get involved but find that uncooperative police officers are not exclusive to Britain.

With another aid worker now dead, the pathologists are trying to piece together just what Rachel was up to. Dr. Andrews tells them that Rachel had been trying to trace the source of an infectious disease that she believed had been affecting many of the local villagers. She had originally believed that the disease was water-borne but all tests had proved negative and was therefore looking at other possible sources. Yet another death however strikes the local ex-pat community. With tensions rising, Nikki finds herself in jail and and Harry getting the cold shoulder from the local coroner.

Nikki and the Lyell unit are called in to investigate an attack against a transgender man.

A mistake has been been made during the course of the investigation, and Thomas is targeted as a scapegoat.