The hugging of a local minister leads DCI Mathias and DS Rhys to a remote mountain community.

As the investigation is brought to a close, Chief Superintendent Prosser confronts an old foe.

Mathias is on the case when the body of a young curator is discovered in a remote woodland.

Tensions arise when an independent investigator is called in to investigate a passing.

Following a fatal shooting, local man Llew Morris is the chief suspect.

Desperate to find the missing boy, DCI Mathias breaks protocol and sets off into the mountains alone. With the clock ticking, Mathias puts his life on the line. But how will his team react, and what will Chief Superintendent Prosser make of his actions? Meanwhile, independent investigator John Powell is put under pressure by retired Chief Superintendent Robert Owen to close the Iwan Thomas case.

DCI Mathias investigates the passing of Catrin John, convicted hugger and former resident of the Pontarfynach Children's Home. As Mathias and Mared investigate Catrin's passing, they begin to suspect it might be linked to the passing of former police officer Iwan Thomas. As Mathias delves deeper into the past, the pressure on him to close the case increases. Will Mathias toe the line or will he risk everything in pursuit of the truth?

The truth about Pontarfynach children's home is about to be revealed by Mathias and Mared, but there is more than one person trying to stand in the way. Will the ugly facts about Dr Hugh Vaughan and the others finally be allowed to come to light? Or will the mystery remain forever buried in Devil's Bridge.