Dr Kate Hanson and the Unsolved Crime Unit are facing their most challenging cold case yet: the year-old murder of a female student.

When, a year after she went missing, the body of 19-year-old student Elizabeth Williams is discovered in a field near her college, Dr Kate Hanson and her colleagues are faced with a seemingly impossible challenge. The badly decomposed remains are offering up few clues, and witnesses are proving either unreliable or reluctant to talk at all.

With little in the way of forensic evidence, Kate realizes that if she is to have any chance of discovering who killed Elizabeth, she must find out what motivated the killer, the reason behind the murder, the why. To do that, she must look beyond what she and her colleagues are being told by those who knew Elizabeth - and into the twisted psyche of a dangerous murderer: a killer whom Kate suspects is ready to kill again.