A young slave, who is also numbered 47 on a plantation in Georgia in the nineteenth century, faces the brutality and injustice of the slavery system.

47 encounters a strange being called Tall John, who appears to be another slave—a runaway. However, as 47 begins to realize, John is an extraterrestrial visitor who believes that his fate is intertwined with that of the young slave.

Tall John is a science fiction creation, but at the same time, he is also a reinterpretation of Tall John the Conqueror—a character derived from old slave myths about a spirit coming from Africa to oppose the slave masters and (ultimately) to free all slaves.