A gay father is found beaten to death and his adopted son is missing. Ronnie and Sam track down the baby's biological parents, a recovering drug addict and her former boyfriend, who are taken into custody. But their stories don't match up so who is guilty of murder and why? Meanwhile, there's tension at the CPS when Kate struggles to view the case objectively and puts the outcome in jeopardy.

Following a break-in, a frail, elderly woman is found dead in her flat. DS Brooks and DS Casey suspect a robbery gone wrong and treat it as murder. Tipped off by the victim's granddaughter, Connie, the investigation turns towards the live-in carer who has gone missing. But the carer, Cecile, claims she was fired because she disobeyed Connie's instructions not to feed her grandmother, and that Connie was starving her to death.

The body of Charlotte Leigh is pulled from the Thames, and after ruling out suicide, Ronnie and Sam focus their enquiries on the victim's abusive ex-­husband with whom she was involved in a bitter custody battle over their teenage daughter. However, the investigation turns closer to home when it appears Holly was keeping secrets of her own. Despite all the evidence pointing to Holly, Jake decides to follow his gut and gambles on a hunch at the trial in a bid to draw out the real killer.

A man is found shot dead in a hotel room and the cash he was carrying has gone missing. Sam and Ronnie learn that the man owed his ex-­wife thousands of pounds in unpaid child support, was lying to his girlfriend about his line of work, and has a son dying of leukaemia, but hadn't been tested for a bone marrow match. Attention turns to the ex-­father-­in-­law, did he hunt down the father of his dying grandson to try to recoup the unpaid money or is there more to this family set up than first appears? At the CPS Jake and Kate try to work through their differences and reach a more even keel.

DS Sam Casey is suspended over the death of Finn Tyler and DI Leyton gets hands on with this investigation, with a reluctant Ronnie as his partner. After a few drinks Jake opens up to new colleague Kate Barker about his mothers' death; Ronnie visits with his estranged daughter; and Sam spends the day with his son.

A suicidal man drives his car across a railway causing a massive train crash and killing over a dozen innocent passengers, but somehow he survives. Crown Prosecutor Jake Thorne pursues the culprit with vigour whilst the man's defence barrister tries to prove his vulnerability and mental illness. Just as the case finishes, CPS Director Henry Sharpe springs one more surprise on Jake… Alesha's replacement. Another new face is DI Wes Leyton, an old colleague of Ronnie's, who is covering for DI Chandler when a suspect is found dead in his cell at court, and the last person seen entering the cell was DS Sam Casey.