Will the police or a devious killer win this battle of wits?

A quiet corner of Wales becomes the centre of a murder investigation when the bodies of a retired couple are found near the shore of a reservoir.

Police try to establish the methods and motives of their attacker by careful examination of the crime scene. And, bizarrely, fishing flies are found in the victims’ mouths.

The investigation into people connected to the area begins to focus on a family farm. But how were the victims connected to it?

When Madog, an elderly member of the small community disappears, the detectives become pretty sure someone on the farm is responsible. But who? And why?

Will finding Madog lead them to the killer? Or have the police themselves fallen into a clever trap?