The Mystery of Manor Hall

I read "The Mystery of Manor Hall".
Manor Hall is an old dark house with a mystery. Nobody can go into the music room. But one night Tom and Milly hear something. The noise is coming from the music room. Tom and Milly open the door. Someone in the music room is singing. Tom and Milly are afraid, but they can't move. What was there...
It's a scary story, but at the end I'm happy with the happy ending.