Gib and the Gray Ghost — Zilpha Keatley Snyder

Gib Whittaker is leaving the Lovell House Orphanage for the second time in his young life. He's going back to live with the Thornton family, who are free to take him in again now that Mr. Thornton has died. Life has changed on the old ranch, and Gib can go to school. But he's still doing all the chores in the barn and stable. He's not exactly farmed-out labor anymore, but will he be adopted for real this time?

Luckily Gib has his beloved horses to care for, especially the beautiful thoroughbred, Black Silk. Then one day a strange horse gallops in out of a snowstorm, a handsome dapple-gray who has been severely whipped and starved. He's frightened and dangerous. Gib knows he must find some way to save this magnificent horse -- and in the attempt, he finds one place where he will always belong.