Spring-Heeled Jack: Man or Fiend (1904) presents, for the first time, the complete text of the final major Victorian serial devoted to London's leaping phantom. Written by Charlton Lea (pseudonym of Alfred Sherrington Burrage) and published by the Aldine Publishing Company between April and September 1904, this twelve-part penny dreadful has long been inaccessible, surviving only in scattered and damaged copies. Edited and introduced by J.S. Mackley, this edition reconstructs the text from British Library and Ohio State University holdings to produce a continuous run for the first time since its original publication. Set in the years preceding the Napoleonic Wars, the story follows Bertram Wraydon, unjustly condemned for espionage, who escapes the gallows only to become enmeshed in a web of treachery spun by his half-brother, Hubert Sedgefield. From the haunted corridors of Wraydon House to the dens of vice in revolutionary France, Spring-Heeled Jack acts as both tormentor and avenger-a diabolical protector whose leaps across the rooftops mark each villain for retribution. The comprehensive introduction situates the 1904 serial at the twilight of the Jack tradition, exploring its overlap with the final alleged sightings in Liverpool that same year and tracing Burrage's influence on later Gothic and adventure fiction. The commentary reveals how Man or Fiend bridges folklore, crime reporting, and melodrama at the fin de siècle, reflecting Victorian anxieties about empire, technology, and moral decay. Lavishly annotated and richly contextualised, this scholarly edition continues The Spring-Heeled Jack Library series, preserving a lost chapter in the evolution of Britain's most enigmatic urban legend.