The Mystery of the Singing Ghost — Gertrude Chandler Warner

One warm night four children stood in front of a bakery. No one knew them. No one knew where they had come from.

Henry, Jessie, Violet, and Benny used to live alone in a boxcar. Now they have a home with their grandfather, and are excited because their cousins are moving to Greenfield.

The Boxcar Children decide to fix up the house that cousins Joe and Alice have bought. There's just one problem. It seems to be haunted -- by a ghost that sings! Is someone trying to keep Joe and Alice from moving in?