Builder David Morris is convicted of the murders. After he's spent 20 years behind bars, a new witness comes forward, sparking a case review.

A new suspect emerges and with his chequered past, the police are convinced they've got their man. But the community isn't so sure.

The police must figure out how to investigate not one, but three of their own when it emerges the prime suspect is a police officer.

What begins as a routine call to a house fire becomes the biggest murder investigation in Welsh history.