As gripping as Room, as powerful as Elizabeth is Missing, Beside Myself is the story of twin sisters, a childhood game with devastating consequences and the slippery nature of identity

Helen and Ellie are identical twins - like two peas in a pod, everyone says.

The girls know this isn't true, though: Helen is the leader and Ellie the follower.

Until they decide to swap places: just for fun, and just for one day.

But Ellie refuses to swap back...

And so begins a nightmare from which Helen cannot wake up. Her toys, her clothes, her friends, her glowing record at school, the favour of her mother and the future she had dreamed of are all gone to a sister who blossoms in the approval that used to belong to Helen. And as the years pass, she loses not only her memory of that day but also herself - until eventually only 'Smudge' is left.

Twenty-five years later, Smudge receives a call from out of the blue. It threatens to pull her back into her sister's dangerous orbit, but if this is her only chance to face the past, how can she resist?

Beside Myself is a compulsive and darkly brilliant psychological drama about family and identity - what makes us who we are and how very fragile it can be.