Detectives Cassie and Sunny reunite as they take on a case concerning the remains of a body found locked in a suitcase in the River Lea. As the pair begin the complicated task of trying to identify the body, the stories of four people with apparent links to the victim begin to unfold. Old wounds are reopened when the detectives track down the victim's wife and son, who have been in the dark about his disappearance for 26 years. Who wanted the man dead and why?

A disturbing allegation about David opens up a second line of enquiry for the team. How much Tessa actually knew about David's life threatens to ruin her relationship with her husband and son. Marion gets into trouble at work and jeopardises her marriage by refusing to open up about her past. After having his phone stolen and information exposed, Colin is blackmailed again - and Sarah's secrets push her family to breaking point.

Having come to another dead end, Cassie and Sunny work on trying to prove a final theory into David Walker's death and catch the culprit.

When the body of a teenage girl who went missing at the turn of the millennium is found at a building site off the M1 motorway, four men are placed under the spotlight and their relationships are tested to the limit.

Cassie and Sunny begin their interviews...

Following the discovery of seemingly incriminating items found at his house, Tim insists he bought them for his girls at a fete in Middenham. However, the team are not buying Tim's story. A new discovery leaves the team shocked and devastated, hitting Cassie particularly hard.