The Mystery of the Stolen Sword — 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 a real apple orchard.

Benny is excited to be spending time at Seymour Curtis's apple orchard. Not only will it be a chance to visit a friend of Grandfather's and help out with the farm animals, but he has heard the orchard is haunted! When the Aldens arrive, they discover that someone has been stealing valuable antiques from the Curtises' home. Whoever it is has even discovered the entrance to the secret passageway where Seymour keeps his collection of swords and suits of armor. Seymour fears the thief may be someone he knows. Benny thinks it is the ghost seeking revenge. The Aldens have another mystery to solve!