Number 47, a fourteen-year-old slave boy growing up under the watchful eye of a brutal master in 1832, meets the mysterious Tall John, who introduces him to a magical science and also teaches him the meaning of freedom.

A young slave boy is named and numbered 47 on a nineteenth-century Georgia plantation and encounters the brutality and injustice of the system of slavery. 47 meets a strange being named Tall John who appears to be another slave boy - a runaway. But as 47 comes to realise, John is an extraterrestrial visitor who believes that his destiny is intertwined with the young slave's. Tall John is a science fiction creation but he is also a reinterpretation of High John the Conqueror - a character taken from old slave myths about a spirit come from Africa to confound the slave masters and (ultimately) to free all slaves.