He came in the early morning, at about half past two. His feet padded along the balcony, slinking silently past the closed doors of the other flats. No one glimpsed his shadow flickering across the curtain or noticed the uneven rhythm of his steps. But he woke Cassy.

And in the morning, Cassy is sent away. She lives with her nan, but whenever the mysterious stranger comes she is packed off to stay with her mother. It's happened before, over and over again, and there's never any explanation.

But this time it's different. This time she is being followed. And the wolf who stalks her through the streets of London disturbs her waking mind and intrudes into her dreams.