When human remains are found by a highway near London, Cassie and Sunny are called to the scene. Dogged work leads the team to a 16-year-old girl who went missing on the eve of the millennium. A close-knit group of old school friends hold the key to what happened. As the four suspects find themselves under the spotlight, their tight bond is put to the test. They all have secrets in their past - events that have pulled their lives apart. None of them are quite who they first seem to be, but is one of them capable of murder? Cassie is determined to correct the mistakes made by the original investigating team - no matter the personal cost.