Unforgotten

Detectives Cassie and Sunny, who find themselves thrown into another historic murder case with the discover of a body. This time it's the perfectly preserved remains of a middle-aged man found in a suitcase in the silt of a London river. As the detectives begin the complicated task of trying to identify the victim, four unconnected people go about their business - Brighton-based lawyer Colin Osborne, paediatric nurse Marion Kelsey, teacher Sara Mahmoud and respected police officer Tessa Nixon - unaware they are about to be dragged into the investigation.

With their victim identified, Cassie and Sunny begin to find out a bit more about David Walker by talking to his ex-wife, DI Tessa Nixon, who reveals he suffered from depression. A search through the original investigation files and some numbers from David's pager help build a picture of him - and also lead to a few potential suspects. However, his son Jason struggles to deal with the news that someone murdered his dad.

Sunny makes further investigations into David Walker's life that suggest he was a troubled man with a number of issues. Marion has a prickly chat with Cassie about her past and the inquiry reveals her close relationship with an IRA activist. As the police investigation encroaches on their life, Sara and Colin open up to their partners with secrets about their past.

Marion jeopardises her marriage by refusing to open up about the past to her husband, Colin is blackmailed even further and the secrets of Sara's past push her family to breaking point. A disturbing allegation about David opens up a second line of inquiry, and when Tessa is called in for questioning again it threatens to ruin her relationships with her husband and son.

Cassie turns her attention to Brentford house and the theory that one or more of the suspects may have been abused at the gatherings there. Marion is questioned again after Sinead's allegation that David could have been an IRA target. The detectives also look further into the accusations made against Colin while he was working in the city - but something does not quite seem to add up. Was his alleged victim telling the truth - and if not, why would she lie?

With the suspects in the murder of David Walker all having either a motive, opportunity or connection to the victim, Cassie and Sunny are left with a massive puzzle to solve. Cassie soon focuses in on Sara, whose alibi seems too perfect, as if it has been put together by an accomplice of the ex-prostitute - and the team is soon investigating the possibility of a wider revenge plan. Meanwhile, interviews with Colin and Marion's loved ones prove revealing.

A look at how this series has progressed from Series 1.

The cast discuss the impact of living a lie.

The cast look at the relationship between the characters in this series.

A look at the set design within the show.

Sam Ives, Art Finisher, explains how the props were created.

A look behind the flashback scenes which provider the viewer with clues.

Sunny reveals the contents of his rucksack!