On the surface, Lara Chorley and Ruth Hull have nothing in common, other than their infatuation with Michael Vokey. Each is writing to a sadistic inmate, sharing her secrets, whispering her worst fears, craving his attention. DI Marnie Rome understands obsession. She's finding it hard to give up her own addiction to a dangerous man: her foster brother, Stephen Keele. She wasn't able to save her parents from Stephen. She lives with that guilt every day. As the hunt for Vokey gathers pace, Marnie fears one of the women may have found him - and is about to pay the ultimate price.