The past comes back to haunt DCI Mathias as he investigates the death of Catrin John, convicted killer and former resident of the Pontarfynach Children's Home. As Mathias and Mared investigate Catrin's death, they begin to suspect it might be linked to the death of former police officer Iwan Thomas. However, independent investigator John Powell is on the cusp of ruling Iwan's death as a suicide - could this change things?

The past comes back to haunt DCI Mathias as he investigates the death of Catrin John, convicted killer and former resident of the Pontarfynach Children's Home. As Mathias and Mared investigate Catrin's death, they begin to suspect it might be linked to the death of former police officer Iwan Thomas. However, independent investigator John Powell is on the cusp of ruling Iwan's death as a suicide - could this change things?

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.

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.

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

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.

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.

The killing of a local minister leads DCI Tom Mathias and DI Mared Rhys to a remote community in the mountains. Confronted by a family in grief and a community in shock, they must tread carefully as they investigate the life and violent death of the troubled victim. As the case continues, DS Sian Owens leads a separate investigation into the recent attack on DCI Mathias, an attack that left his home destroyed and his skull split open. DS Owens's investigation is an unwelcome distraction for DCI Mathias, and he struggles to keep his emotions in check as the two cases unfold.