Johnny Mnemonic is an idiot savant: He stores other people’s secure information in his brain, though he cannot consciously access that information himself. Ralfi Face, a client, wants him dead. To fight back, Johnny goes low-tech by creating an old-fashioned gun. The story’s central theme is that superior technology does not defeat one’s enemy; what is needed is the best use of the technology one chooses.
Ralfi catches Johnny offguard despite the gun, but razorgirl Molly intervenes on Johnny’s behalf. Ralfi explains that the information in Johnny turned out to be stolen from the yakuza, who do not want anyone else to obtain it through squids, a program that cracks idiot savant security. When Ralfi is killed by a vat-grown yakuza assassin posing as a tourist, Molly takes Johnny to Nighttown and the Lo-Teks, a gang who have forsaken high technology for more primitive means. For blackmail purposes, they unlock the yakuza information through Jones, a drug-addicted dolphin with cybernetic enhancements. Molly then confronts the assassin on the Lo-Teks’ ritual Killing Floor: The two perform dancelike moves until the assassin falls to his death, as Molly “killed him with culture shock.”
A year passes as Johnny and Molly live with the Lo-Teks, working with Jones to draw old client information from Johnny’s head and use it for profit. Now realizing the emptiness of his past life, Johnny hopes to clear out all that information eventually and retain only his own memories. Though this story ends well for Johnny, his later death at the hands of another assassin is recounted by Molly in Neuromancer.