Final appearance of Sam Casey.
A suicidal man drives his car across a railway crossing causing the train to crash and killing twelve people. The investigation takes on several twists as the law and order teams pursue the case with vigour and determination to uncover the truth of the situation.
DS Sam Casey is suspended over the death of Finn Tyler and DI Wes Leyton gets hands on with this investigation, with a reluctant DS Ronnie Brooks as his partner. After a few drinks Jake opens up to new colleague Kate Barker about his mothers' death. We meet Ronnie's estranged daughter and follow Sam as he spends the day with his son, giving new insight into our heroes' off-duty lives.
A man is found shot dead in a hotel room and the cash he was carrying has gone missing. We discover the man owed his ex-wife thousands of pounds in unpaid child support and was lying to his girlfriend about his line of work. DS Casey and DS Brooks also learn he has a son dying of leukaemia, but hadn't been tested for a bone marrow match. Attention turns to the ex-father-in-law, Philip Donovan. 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 work out their differences and reach a more even keel.
The body of Charlotte Leigh is pulled from the Thames. After ruling out suicide, DS Brooks and DS Casey focus their enquiries on the victim's abusive ex-husband Richard with whom she was involved in a bitter custody battle over their teenage daughter, Holly. However, the investigation turns closer to home when it appears Holly was involved in a relationship with her mothers' new husband, Sean. Despite the evidence pointing to Holly, Crown Prosecutor Jake Thorne follows his gut and gambles on a hunch at the trial in a bid to draw out the real killer, and in turn uncovers the dark truth behind the façade of a seemingly perfect family.
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. Further investigations throw more suspicion on the granddaughter who is charged. Despite her brief arguing that it is impossible to prove Connie is responsible for her grandmother’s death, Chief Prosecutor Thorne has the bit between his teeth when he tells the jury Connie was the only real family the victim had, and she left her to die.
A gay father is found beaten to death and his adopted son is missing. DS Brooks and DS Casey track down the baby’s biological parents, Ruth Pendle, a recovering drug addict, and Neil her former boyfriend, who are taken into custody. But their stories don’t match up so who is guilty of murder and why? And there is tension in the CPS offices when Kate Barker struggles to view the case objectively and puts the outcome in jeopardy.