To mark the release of the Nicole Kidman, Colin Firth and Mark Strong-starring thriller Before I Go to Sleep in cinemas this Friday, September 5, we're giving you the chance to win the SJ Watson thriller on which it is based.

Before I Go to Sleep tells the story of Christine (Kidman), "a woman who wakes up every day remembering nothing - the result of a traumatic accident in her past - until one day, new terrifying truths emerge that force her to question everyone around her".

To be in with a chance of winning the book, just answer this question:

What is the name of Nicole Kidman's character in Before I Go to Sleep?

Send your answer, name and address, marked Sleep Comp, to: One entry per person. Closing date: Friday September 5.