When Cassie immerses herself in a undercover assignment, threats both known and unexpected haunt her every living breath. Rob desperately hunts down one last lead.

In the summer of 2006 detectives Rob Reilly and Cassie Maddox are sent to investigate a child’s murder. They find a community caught between the old Ireland and the new.

Despite Rob’s promise to Cassie that they won’t investigate Operation Vestal, they make a dark bargain to keep the secret and carry on working on the cases.

All of Knocknaree mourns as Katy Devlin is laid to rest, while the pressure on Rob and Cassie mounts as there are still no arrests in the case.

As Cassie struggles to make sense of Lexie’s life and death, we delve into her own difficult past. Meanwhile, Rob’s past finally yields some results in the Katy investigation.

Rob makes costly mistakes as Cassie immerses herself in the art of being Lexie.

The finale finds Rob and Cassie forced into a face-to-face reunion.As arrests are made, Rob and Cassie both come to profound realisations.

Everything comes to a head as Cassie confronts Lexie’s killer and Rob has a breakthrough about Katy’s murder.