The Color of Your Skin Ain't the Color of Your Heart by Michael Phillips

Orphaned by the Civil War, Katie, the daughter of a plantation owner, and Mayme, a former slave, have worked hard to keep Katie's plantation going, all the while hiding the fact that they are alone. Now the girls face new threats to their way of life: mounting floodwaters...and mounting danger from thieves. When a long-lost relative appears, he disappears as suddenly, taking their closely guarded secret with him. But this man has a secret of his own -- one that will change them all forever...