Detective Chief Inspector Ryan retreats to Holy Island seeking sanctuary when he is forced to take sabbatical leave from his duties as a homicide detective. A few days before Christmas, his peace is shattered and he is thrust back into the murky world of murder when a young woman is found dead amongst the ancient ruins of the nearby Priory.

When former local girl Dr Anna Taylor arrives back on the island as a police consultant, old memories swim to the surface making her confront her difficult past. She and Ryan struggle to work together to hunt a killer who hides in plain sight, while pagan ritual and small-town politics muddy the waters of their investigation.