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.

The team assists DI Paul Renick following the assumed suicide of Jamal Al Sham and discover that he was murdered and was a people smuggler, blamed by Varkey Khoury, head of a family of Syrian refugees, for killing his wife. Varkey's 15 year old daughter Akka approaches Nikki for news of her mother, leading to Nikki sheltering her whilst the police haul in another young woman Tamara as a likely killer. At the refuge camp in Calais apparent altruist Yusuf Hamed assists 12 year old Sosa to come to England whilst Kalil Aziz, an associate of Sham, is also murdered and the police and pathologists make a grim discovery in an English forest.

The pathologists join the police in removing the corpses of the refugees who suffocated in the locked van and find a possible clue in phone messages sent by the dying victims. Whilst a customs officer due for retirement is suspected of allowing the people smuggling the team establish that the culprit took money from the relatives of the migrants he then left to die, Akka's mother among them. Yusuf rescues another batch of refugees from a second locked van, escaping with Sosa before the police arrive but the real clue surfaces via a Syrian charity to which the killer donated the victims' monies.