Lynda Graham has been fortunate in life. She is happily married, with two wonderful children, Ciarn and Katie. She has a beautiful home and garden in one of the most affluent suburbs of Dublin. Her world feels safe and uncomplicated, one she now takes for granted. That is until Jon, a friend of Ciarn's from university - handsome, charming and clever - inveigles his way into their lives.
There's something about Jon that Lynda finds unnerving - he is almost too perfect. And her instinct is right: Jon's arrival sets in motion a spiral of events that contributes to the gradual disintegration of all she holds dear.
When Jon leaves, his disappearance is even more destructive than his presence. Lynda's quest to track him down reveals unpalatable truths about his past and the reason for his existence in their lives. Lynda knows that Jon is out there somewhere - watching, waiting, malevolent.
And she also knows that she must do whatever it takes to protect the most precious thing she has - her family.