After blowing the whistle on a colleague Detective Grace Narayan is sent to a small Welsh island; there she encounters local GP Doctor Pridaux who explains that his son Cai vanished a year ago, but the investigation proved fruitless.
An identification is made of the body and Grace is keen to prove it was murder, but a murder investigation team arrive from the mainland and take over proceedings.
Grace is adamant that Gruffudd is somehow involved in Cai's death, and she tries to get to him, through Minh; Doctor Pridaux provides Grace with a credible lead after spotting a detail in the photograph.
Owen and Winter think they're helping the case by conducting an illegal search of Gruffudd's house, but their actions prompt an angered response from an exhausted and unwell Grace.
Grace learns exactly what's happening on the island and all the questions that she had about The True Way are answered; the murderer is brought to justice.
Police sergeant Grace Narayan uncovers a cold case, pagan worship, and a community bound by eerie rituals on a remote island.