Harry's work colleague Justine Thompson is murdered in her house with her daughter Gemma whilst her stepson Charlie, also attacked, lies in a coma. Baby daughter Ellie, however, is unharmed. Husband Stuart is prime suspect but he has an alibi and his grief seems genuine. The post mortem shows that Gemma was pregnant and the team learns that Justine once needed a restraining order against Stuart's brother Kevin, who was obsessed with her. Mrs Barron, the lady from next door who found the bodies, finds evidence on her son Joel's computer that Gemma and Charlie were lovers as Joel rides off to see Kevin.

After Kevin dies in a motorcycle crash Harry is surprised to see Joel keeping a vigil by Charlie's hospital bed. Whilst denying murder Joel professes that he loved Gemma was shocked that she was sleeping with Charlie. Stuart's initial alibi breaks down when CCTV footage shows Kevin, not him, at the hotel in question but he admits to an affair with Mrs Barron. The murderer is eventually exposed after a shocking betrayal is revealed, leading to an horrific reaction.