The Roundhill - Dick King-Smith

A time-warp ghost story set in 1936. Evan, an only child, always looks forward to the school holidays when he rides his bike to the Roundhill - a magic place he can see from his bedroom window. One summer he meets a girl in strange clothes who appears and disappears in a mysterious fashion. Gradually Evan accepts that she must be a ghost. Later he turns detective and discovers she is the ghost of Alice Liddell - the original Alice in Wonderland - returning to a place she once visited and loved in childhood. Even stranger, Alice stayed at Evan's house and the room she slept in was Evan's bedroom.