Still wracked with grief at the death of his colleague, River's mental fragility is further strained as he begins to suspect that the man he chased to his death was innocent.

The discovery that Stevie was keeping secrets forces River to reassess how well he knew his colleague and friend. Unlocking her voicemails throws suspicion on somebody close to Stevie; somebody with real motive and a history of violence.

The investigation into Stevie's murder changes direction when CCTV footage shows her to be closely involved with an illegal immigrant who owned the car that was used in her murder. The police launch a manhunt to track him down.

When River and Ira uncover what Stevie was investigating before her murder, it leads to the discovery of a new suspect. But breakthroughs in the case have devastating implications for another member of the team.

As the fractured events of Stevie's murder start to swim into focus for River, the awful truth places more pressure than ever on his worsening state of mind. Can he carry on when so much is left unsaid?