On his first day on a new job DCI Tom Mathias investigates a blood soaked bathroom and the disappearance of 64 year old Helen Jenkins. The inquiry focuses on an old Children's home above the ravine spanned by the Devil's Bridge.
A body is found in the depth of a flooded quarry near the remote village of Penwyllt. The investigation tries to discover who he was and if his death was an accident.
The body of a young woman is found abandoned but carefully placed in the marshes. This case, in the series finale, pushes DCI Mathias to the edge, both personally and professionally.