From the moment Katy sees Genevieve's beautiful face staring at her from a window, her life will never be the same. Wherever Katy turns, Genevieve is there - at school, with Katy's friends, and worst of all, in Katy's hot new boyfriend's life.

But Genevieve has a menacing side, a dangerous side, a threatening side that she only reveals to Katy: I'm your worst nightmare.

When Genevieve's behaviour becomes increasingly twisted, Katy delves into the girl's past, with the help of her best friend Luke. Nothing prepares her for the dark truths that she discovers, or the new romance she finds along the way. Is Genevieve a troubled girl with a difficult childhood? Or is the truth unearthly and much more frightening?

Who is the real Genevieve?

What are her secrets?

Why is she determined to destroy Katy's life?

A rich, twisting thriller of friendship, love and evil that you'll find impossible to put down.

There are 352 pages in this book. This book was published 2012 by Hachette Children's Group .

Siobhan Hayes spent her formative years at a Catholic convent school in Crosby, Merseyside. Later she studied English at university and worked for the civil service. Her time is currently spent writing and working for the family business, but she spends much of the time escaping for long walks by the sea.