Magic by the book

Neither Anne nor Emily remembered choosing the book at the library, but when as they read it, the boundary between their world and the one described in the book disappears. Suddenly they are in Sherwood Forest, where they join Robin Hood's band. The further adventures that await Anne, Emily, and their brother, Will, are the kind they had always dreamed about. They had yearned for magic as strong as the spell cast by the stories they loved best. But then an uninvited guest turns up at their parents' garden party. The sinister man snatches the book with the intention of using its powers for evil, and the siblings find themselves engaged in a battle to regain possession of the book.