The police investigate an apparent break-in that results in the death of Derek Irons, his wife and youngest daughter. Two older children survived the attack but one is in serious condition and in a coma. Irons was a ruthless businessman who targeted his rivals' customers resulting in regular confrontations. Irons was stabbed but his wife and daughter were shot. Sam is reunited with an old friend from Northern Ireland, Det. Supt. Tony Ashton who is the senior investigative officer on the case. Harry assists the police with the death of an old woman who is believed to have fallen down a staircase. His post-mortem reveals evidence that is not consistent with a fall.

The police continue their investigation into the deaths of several members of the Irons family but based on the forensic evidence, they now believe he may have been killed elsewhere and then transported to his home. When one of Irons' two surviving children is killed, they look to his circle of friends and family for a possible motive. Thanks to Harry's information, the police investigate further into the death of an elderly woman who supposedly fell down the stairs in her home. Supt. Tony Ashton clearly wants to renew his friendship with Sam but she isn't so sure. Leo's home life is in turmoil and it's been affecting his work.

When Nikki sees barefoot teen-ager Shannon Kelly run over by a car whilst fleeing somebody she sits with her until the ambulance arrives and later visits her in hospital,where it is clear she is frightened of a man. DS Masood tells Nikki Shannon has been sexually abused and suspects Abdul,her estranged stepfather. Shannon turns up at Nikki's and reluctantly agrees to go back to hospital. Meanwhile a gang of young Asian men are picking up and grooming white school-girls for the sex trade. They already have Shannon's friend Amy and go after two more,Hannah and Lauren. The pathologists investigate two seemingly unrelated cases - the remains of a young girl found in discarded airport luggage and a heavily tattooed man,John Dear,who died of toxic poisoning. Then a third corpse is found - that of Amy.