A space shuttle mission investigating Halley's Comet brings back a malevolent race of space vampires who transform most of London's population into zombies. The only survivor of the expedition and British authorities attempt to capture a mysterious but beautiful alien woman who appears responsible.
A notice in a newspaper seeks red-headed men, inviting them to join a league which will pay them well - and Jabez Wilson, a pawnbroker who responds, finds he is hired and paid generously for spending four hours a day copying an encyclopedia in long hand. When the league is suddenly dissolved, Holmes is asked to find out what has been going on, and he quickly suspects crime. Indeed, behind this curious arrangement lurks Holmes's arch-enemy, Professor Moriarty.