Laura Dean, a curator, is discovered in a shallow grave in remote woodland. Mathias and his team must delve into the young victim's life to unearth some shocking secrets. Meanwhile, Prosser - still reeling from the death of Iwan Thomas - calls on the help of retired Chief Inspector Robert Owen.

Following a fatal shooting at a remote petrol station, local man Llew Morris is identified as the chief suspect. Determined to find the killer, DCI Mathias and DI Rhys visit the house where Llew grew up and make a gruesome discovery which cements Llew's guilt. Tensions escalate even further when news arrives that Llew's young son has disappeared from his school.