A waterlogged suitcase holds the remains of David Walker, 25 years after he disappeared. Walker’s wife, Tessa, turns out to be a police officer. Cassie and Sunny interview two other suspects, Sara and Colin.

Detectives Cassie and Sunny begin to find out a bit more about who David Walker was through speaking to his ex-wife Tessa. A search through the original investigation files and numbers traced from his pager help them build a picture of David, and lead them towards potential suspects. A conversation with David's old school friend leads Cassie and Sunny to believe that they may have found a motive.

Further examination of David Walker's history suggests that he was a troubled man with a number of issues. Marion has a prickly chat with Cassie about her past and the investigation reveals her close relationship with an IRA activist. As the police enquiries encroach on their lives, Sara and Colin open up to their partners.

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.

Cassie begins to investigate the Brentford house and the theory that one or more of the suspects may have been abused at the gatherings that took place there. The enquiry reveals some information that allows Colin to come to terms with a shame that he has lived with for over 25 years. Sara is forced to confront her past in order to prove her innocence. Marion pushes her family even further away.

As each of the suspects have either a motive or a connection to David Walker, Cassie and Sunny work on trying to prove a more far-fetched theory that involves travelling across the country and delving further into the past of the suspects.