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.

At a remote farmhouse, sixty-nine year old Idris Williams is discovered bludgeoned to death, and the investigation into his murder reveals the mountain’s bloody past.

In the isolated village of Penwyllt, the body of a young man is discovered in the murky depths of a quarry lake. But who is he, and was this 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.

Mathias is under pressure. His wife Meg has turned up in Aberystwyth and he's under investigation by the IPCC following the death of Mari Davies at the end of the last episode. When a bus driver is found shot dead on an isolated mountainside, the investigation provides a welcome escape.

The murder of a local dignitary and barrister leads to the uncovering of a tragic story of love and loss fuelled by mistrust and suspicion in the depths of the Hinterland. Why were Nora and Daniel living such a secluded life? What has Mathias discovered in the garden? Will he find Daniel before Glyn Powell gets hold of him? The clock is ticking, but Mathias knows that the relationship between Branwen Powell and Daniel is key to uncovering the truth.

The discovery of a body in a remote lake leads Mathias and the team to investigate the complicated private life of a teacher missing from a small rural school.

DCI Mathias must solve the case of the murdered Aron Bowen, but he must deal with feuding family members and runaway teenagers first. Will he discover the truth of the matter or will the person that's stalking him get in his way?

DCI Tom Mathias and DI Mared Rhys are confronted by a family in grief and a community in shock when they investigate the violent death of a local minister.

As the investigation into the murder of a local minister continues, the net tightens around the minister's daughter. And as the case is brought to a shattering close, Chief Superintendent Prosser is forced to confront an old foe.

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.

With time running out, Mathias must solve the mystery of Laura Dean's death whilst trying not to get distracted by his personal problems.

A local man is the chief suspect in a fatal shooting at a remote petrol station. Tensions escalate when the suspect's young son disappears.

Desperate to find a missing boy and his killer father, DCI Mathias breaks protocol and sets off into the mountains alone. With the clock ticking, Mathias puts his life on the line.

The past comes back to haunt DCI Mathias as he investigates the death of convicted killer Catrin John - could her death be linked to that of Iwan Thomas's?

The past comes back to haunt DCI Mathias as he investigates the death of convicted killer Catrin John - could her death be linked to that of Iwan Thomas's?