#8 The Black Jacket Mystery by Kathryn Kenny, 1961.

Trixie and the other Bob-Whites are concerned about their pen pals in Mexico because an earthquake has damaged their town. To help them rebuild their school library, the Bob-Whites decide to hold a benefit carnival to collect books.

While they are planning the carnival, Trixie becomes worried about Regan, who is in charge of Mr. Wheeler’s stable. She overhears him speaking to her mother about a problem, asking her advice, but saying that he doesn’t want the kids to know. Although Trixie doesn’t want to pry to into Regan’s business, she can’t help but worry about him and wonder what he doesn’t want them to know.

Then, a boy called Dan Mangan comes to live with Mr. Maypenny. Dan wears a black jacket and looks like a member of some kind of street gang. At school, he brags about brushes with the law. The Bob-Whites try to be friendly with him, but something about Dan gets on Trixie’s nerves.

When someone sells Honey’s missing watch at Mr. Lytell’s store, people begin to suspect that Dan may be a thief. But, soon, Trixie and the others start to suspect that someone else may be hiding out in the woods.

The book is currently available online through Internet Archive.