Cassie and Sunny catch another historic murder case with the discovery of a body in a suitcase at the bottom of a London river. As the detectives try to identify the victim, four unconnected people go about their business: lawyer Colin Osborne, nurse Marion Kelsey, teacher Sara Mahmoud, and police officer Tessa Nixon -- all unaware they are about to be dragged into the investigation. UK Edition.

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. UK Edition.

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 lives, Sara and Colin open up to their partners with secrets about their past. UK Edition.

Marion jeopardizes 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. UK Edition.

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. The detectives also look further into the accusations made against Colin -- but something does not quite seem to add up. Was his alleged victim telling the truth -- and if not, why would she lie? UK Edition.

With the suspects in the murder of David Walker all having either motive, opportunity, or a 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 -- and the team is soon investigating the possibility of a wider revenge plan. Interviews with Colin and Marion's loved ones prove revealing. UK Edition.