Detectives Rob Reilly and Cassie Maddox are on the case after a young girl is found murdered in the woods on the outskirts of Dublin, Ireland.
Rob and Cassie make a dark bargain to keep the secret and solve the cases.
All of Knocknaree mourns as Katy Devlin is laid to rest; the pressures on Rob and Cassie mount as there are still no arrests in the case.
As Cassie struggles to make sense of Lexie's life and death, her own difficult past comes to light; Rob's past finally yields some results in the Katy investigation.
Cassie prepares for the most challenging investigation of her lifetime; Rob hits rock bottom.
When Cassie embeds herself in Whitethorn House, threats both known and unexpected haunt her every living breath.
Everything comes to a head as Cassie confronts Lexie's killer and Rob has a breakthrough regarding Katy's murder.