Girl In The Attic by Valerie Mendes
Thirteen-year-old Nathan is furious when his mum hauls him off to Cornwall for Christmas and then tells him they are to move there for good. He wants to be back with Dad, with his best friend, Tom, in his London life. But then he finds a cottage - and a girl. The girl in the attic. Who is she and what is the family secret that haunts her life?