Following a court appearance for drunk driving, Leo is required to perform unpaid work as a punishment, assisting AJ, a community worker on a run-down,largely black-occupied housing estate in South London. AJ is hoping to divert boys away from crime by encouraging them to do sports, and, though initially dismissive of Leo as a white intruder, comes to respect him after he has saved the life of Errol, a former gang member now anxious to keep his little brother Levi out of trouble. Errol has been stabbed in the leg by members of a gang from a rival estate and Leo stops him from bleeding to death. Earlier in the week a young girl called Shana Block was stabbed to death at a funfair and her murder recorded on a mobile phone. As Shana lived on the estate police sergeant Wallace involves Leo as a go-between with the suspicious residents. Also on the scene are Harry and Nikki, the latter dating Ryan, a young Scottish paramedic she met when called to the scene of Shana's death. Before any arrests can be made, Richard Ojana, a member of a rival gang, is shot in broad daylight and nobody is willing to come forward as a witness. Believing he knows who the killers are, Errol goes off into the night, but the next day his corpse, tarred and feathered, is dumped on A.J.'s recreation ground.

The examination of the latest body from the housing estate proves it to be that of Errol Harris who was asphyxiated while being tarred and feathered. The policeman in charge of the case, DS Nick Wallace, is exasperated at the lack of physical evidence the pathologists are able to provide him as without concrete proof of who is involved in the killings, he knows they will never get a conviction. Leo Dalton thinks that the key to getting information is Errol's younger brother Levi who is actively being recruited to join the gang. Tragedy ensues however after the police question the boy. Finally at their wit's end, Leo comes up with a piece of evidence that has been available from the very beginning of the case.

The team is called in to identify the corpse of a woman whose face was surgically removed after death. Janet Mander, a Home Office anthropologist, cannot link it to similar murders but, after Nikki has reconstructed the face, Holly, a medical student on work experience with Harry,recognizes the woman as Fran Price, an investigative journalist. Pargeter, her agent, is evasive and Supt. Barker, the investigating police officer, does not help as he is obsessed with the idea that Leonid Polyak, a Russian criminal Fran helped to put behind bars, has ordered a hit on her from his prison cell. Whilst Leo gets closer to Janet, Harry is concerned when he sees Barker entering Holly's flat and later she is found murdered in her bed.

Everyone is affected by Holly Farr's murder. The pathologists find that she was tortured and beaten but died from having her throat slit. The police believe that her death is related to that of Fran Price and the recent leaks of forensic evidence to the press may have led the killer to her. Supt. Barker decides to put armed policeman to guard each of the three pathologists but Harry Cunningham, who saw Barker go into Holly's house, is suspicious of his true motives. When a prominent Russian, Oleg Kolik, seeks asylum in the UK saying he is the true target of the Russian assassins, Harry thinks that Fran Price may have been targeting him in her new book. When Leonid Polyak is murdered while being transferred between prisons, he decides it's time to put his job on the line in the pursuit of justice.

The team is called in after Mr. Stickley of the Police complaints Board feels that something is not right about an armed police raid on a house where several people were killed, including one of the officers and a mystery woman. A young Muslim called Melik has been badly wounded and lies in hospital. Mr. Stickley believes the policeman was killed by Rhys Allen, a colleague who was having an affair with the deceased's wife. Melik's sister Isra confides in Nikki that all the 'suspects' were unarmed and not terrorists and fears of a cover-up by the authorities are not helped by the aggressive attitude of Inspector Transfield, particularly when Nikki is attacked and evidence stolen from her laptop.

Harry Dalton and DI Helen Okoroafor manage to identify the dead woman from the scene of the raid - who turns out to be a DS who was working undercover and who the police refused to identify when the pathologists submitted her DNA sample to them. While DI Tranfield continues to search for the terrorist cell that he is sure is about to strike, Nikki Alexander continues to try and piece the evidence together from the scene of the raid but clearly there are pieces missing. A re-creation of the shooting shows her what happened and also identifies the only person in the right position to have shot the police officer.

Harry Cunningham investigates the death of a young Orthodox Jew. He accedes to the family's request that he not use invasive procedures in his examination and finds that the young man was savagely kicked and beaten to death. DI McKenzie has a suspect in custody but from what medical and forensic evidence Harry is able to find, with Nikki Alexander's assistance, it's obvious that the family is lying about the young man's whereabouts the night he was killed. Leo Dalton meanwhile investigates the death of a young student who died from a drug overdose. Leo is uncomfortable with what he finds, particularly that she had sex with one of the men at a party when her boyfriend was in the next room. He thinks she may have been given GHB.

With a second member of the Orthodox Jewish community dead, Harry performs a complete examination. This time, Harry does not hesitate to use all examination methods at his disposal and finds forensic evidence that clearly links a third member of the Hassidic community to both deaths. After DI MacKenzie makes the arrest however, Harry realizes he may have inadvertently contaminated the DNA evidence leading to a false result. Nikki retests all of the evidence and together they figure just who the attacker was. Leo Dalton meanwhile tries to prove that the dead student had been given GHB. He concludes that someone also tried to administer CPR.

The half-naked corpse of a twelve-year-old boy is found in his school grounds and Liam, the child in whose company he was last seen, has disappeared. Nikki is particularly involved because the school's head teacher,Noel Hopkins, is the teacher who, years earlier, encouraged her interest in science.

A severely mutilated corpse is found on a railway line, belonging to a known paedophile in his twenties, Francis Neil. Noel Hopkins is arrested, following revelations years earlier of an affair with a young pupil Nikki believes to be Francis but he is released due to insufficient evidence, though he is sacked from his job and his house torched, his saviour being Danny, father of the dead boy Michael. It is ultimately revealed that in fact Liam did not exist - he was the 20-something Francis, obsessed with Michael, and both were victims of the paedophile ring. Ultimately Nikki helps Noel to overcome prejudice and regain his job.

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.