The Floating Circus by Tracie Vaughn Zimmer
Twelve-year-old Owen forgoes an orphan train that's headed west only to find himself falling in with a completely unexpected group of misfits—circus performers on the River Palace. As this floating circus makes its way down the Mississippi, Owen slowly discovers that his fellow workers aren't freaks, but loners, like he is. A brush with yellow-fever in New Orleans and a devastating storm threaten the boat and its passengers. But it's the menace of slave catchers that poses the greatest danger of all, and will put Owen's loyalty to a freed black man to the test.