Jack's world is blown apart by the discovery of Hannah's dead body. Nikki uncovers the truth behind Jack and Ryan's strained relationship, but Jack's attempts to find evidence put his job at risk. While an angry Thomas wrestles with hiring forensic scientist Helen as Jack's permanent replacement, Dr Christy Nash fears for his marriage and business when DI Carter learns of his relationship with 15-year-old Katie. As Jack's suspicion of Ryan grows, his lone investigation puts him in grave danger and life will never be the same again.

Following the shocking discovery of a 15-year-old girl's body, DI Dale Carter fixates on his prime murder suspect, Ryan Kelvin. However, Jack's personal connection to Ryan presents a conflict of interests, leading Thomas to replace him on the case with forensic scientist Helen Ferguson. But in his quest for the truth, Jack is instinctively drawn into the investigation, alienating him from Nikki and the team. Hannah, the distraught best friend of the victim, becomes consumed with grief and guilt over the murder, leading her to take drastic action.

Martin, the sole eyewitness in the murder case, is found dead in suspicious circumstances. Threatened by an angry Bekir, Nuri grows increasingly desperate to find the missing drugs, with tragic consequences. Nikki helps grieving William come to terms with his daughter Alice's death and his missing baby granddaughter.

Under pressure from his wife Ellie, DI John Brooke finally comes face-to-face with his nemesis, drug dealer Bekir. However, Jack's growing frustration over DI Brooke's meddling in the case unearths a new line of enquiry.

When the body of a pregnant Northern Irish girl is discovered, the team face the urgent task of finding the baby snatched from her womb. The child's father, married man Simon, is the prime suspect in DS Sally Kirchner's eyes.

Meanwhile, Thomas uncovers the teenage girl's connections to a criminal underworld. Nikki and Jack encounter her addict boyfriend Nuri and ruthless drug dealer Bekir, suspected of masterminding the killing of a Drugs Squad cop. The dead detective's partner, DI John Brooke, is out to avenge his colleague's murder.

Nikki, Jack and DS Ross find themselves under pressure to urgently close the net on a serial killer abducting young women. Concerns grow over missing Sarah, and solving her mysterious disappearance becomes an urgent priority for Nikki and Jack. Local huntsman Niall Wallace makes a surprising admission under questioning from DS MacNeil. However, Nikki's confidence in the detectives is diminished when she suspects a cover-up in the past case of a murdered prostitute and her pimp.

Nikki and Jack head to Scotland to help earnest rural detective DS Jason Ross investigate the chilling murder of a lap dancer found in a remote forest. In their search to find a suspect, the team clash with rogue city detectives DS Mike MacNeil and DI Simon Laing. But as more human remains are unearthed in the forest, it becomes horrifyingly apparent that a dangerous serial killer is at large. News of the murders unsettles new mother Sarah, who is harbouring a dark secret from her partner Steve.

Nikki's professional reputation is on the line when her romantic involvement with lawyer Greg Walker leads her face-to-face with a raging Bennetto. Thomas is under mounting pressure from DI Rachel Klein and the Home Office as he battles to save the Lyell Centre's reputation in the midst of a media storm.

Grieving for the death of his murdered son, newspaper hack Peter Masham strikes an unlikely deal with Bennetto's brother-in-law. Meanwhile, Jack and Clarissa uncover the true identity of murder victim Byron Lee.

Nikki delivers ground-breaking testimony in the high-profile appeal court case of David Bennetto, a convicted killer who has spent the last six years behind bars for the murder of two gay teenagers. But bitter DI Rachel Klein remains unconvinced that she caused a miscarriage of justice and cannot hide her contempt, especially when another young man is found dead bearing the same hallmarks of the previous murders. Meanwhile, Nikki's professionalism is brought into question due to her increasingly close relationship with lawyer Greg Walker.

Footballer Isaac Dreyfus desperately fights to prove his innocence, whilst disillusioned Adam Freedman turns to a mysterious source for help to avenge the murder of his wife and child. Under scrutiny from the press, the police are determined to nail their prime suspect and pile pressure on The Lyell Centre to deliver results. However, when Nikki questions the motive behind the murders, a re-examination of the Freedman crime scene leads Jack to make a startling discovery.

Top-flight footballer Isaac Dreyfus' days at the top are numbered when a sex tape links him to the brutal murder of a young woman, threatening to destroy his reputation and marriage. Nikki struggles to come to terms with Leo's death following the arrival of the new Lyell Centre boss, pathologist Thomas Chamberlain. However, her feelings surface when DI John Leighton and DS Anne Burchett demand results in two unsolved cases - a mother and son murdered in their wealthy London home and the disfigured body of a young woman.