The Outer Space Mystery — 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 they are visiting an observatory.

The Boxcar Children are going to college! That is, they are going to Mountvale College to help Grandfather at a convention of young astronomers. The Aldens learn many interesting things, and get to look at the stars and planets through a telescope at the observatory. But then some valuable information disappears - along with one of the students at the convention! What's going on? It's another mystery for the Boxcar Children!