47 by Watler Mosley

From chapters.ca:
A gripping YA fiction debut by bestselling author Walter Mosley. Walter Mosley is one of the best known writers in America. In his first book for young adults, Mosley deftly weaves historical and speculative fiction into a powerful narrative about the nature of freedom. 47 is a young slave boy living under the watchful eye of a brutal slave master. His life seems doomed until he meets a mysterious run-away slave, Tall John. Then 47 finds himself swept up in a struggle for his own liberation.