A swarthy villain, nearly seven foot tall and presumed hanged, seems to wake from the dead in the presence of young Bartholomew Dorking. Having outwitted the noose, Black Jack enlists the unwilling boy to be his companion. Together they weave their way through the seamiest parts of old London, a traveling circus, and a private madhouse where forgotten lunatics are chained in empty rooms, and from which Bartholomew rescues Belle, a girl who may not be mad at all.