The horrors of World War I have robbed returning veteran Chris Baldry of his memory. The traumatized soldier doesn't even recognize his own wife, Kitty, or remember their years together. While Baldry attempts to cope with the unfamiliar surroundings of his own home, he seeks out the company of an old flame from his childhood, Margaret Grey. His amnesia also makes him a ready target for the affections of his older cousin, Jenny.
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.
The police are baffled by the murder of Willoughby Smith, and Inspector Hopkins looks to Holmes to solve the case.