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.

Pregnant Karen Sawyers is murdered and her blood-stained husband Pete found wandering the streets but DI Naomi Silva turns her attention to Karen's lover, Adam Hayes, who was treating her at his clinic and had arranged for her to have a termination. Then Adam is also found dead. Clarissa finds evidence that Karen was being blackmailed with threats of Pete getting her medical records. This leads Naomi and Nikki to hospital head Simon Laing, who tells them a computer hacker calling himself Splinter stole patients' files though Simon kept it quiet for fear of tarnishing the hospital's reputation. Meanwhile barrister Jason Farrell is viciously attacked and left to die.

With Jason in a coma the police, given his hospital attendance, assume he was Splinter's latest victim though he was not robbed. A known hacker Gary Brockham is arrested and admits to selling hospital files on the dark web whilst Laing must admit his use of a questionable computer system company. He too is killed before a secret from the past resolves the case.