The Madman of Piney Woods by Christopher Paul Curtis
My rating: 3 of 5 stars
If you loved Elijah of Buxton you'll enjoy this chance to revisit the town and see what happens 40 years later. If you didn't love Elijah it's probably because you haven't read it yet - so go do so after you read this companion novel. It doesn't matter, really, which order you read them in.
The titular Madman is, of course, isn't as Big and Scary as a one might assume from the title; he is, on the other hand, a necessary means to bring the two main characters together. As a work of historical fiction this is less jarringly "other", and the adventures the boys have will seem familiar to adults reading this with their middle grade readers.