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.

A body is identified. Grace is keen to prove it was murder.

A huge storm hits the island, forcing Grace to spend time with all the locals under the same roof; Grace continues to investigate Cai's death; Silas provides an interesting lead, The True Way.

Grace is adamant that Gruffudd is involved in Cai's death.

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.