Des' sense of self is thrown into confusion when Netta, Cuddly and Miss Griffin all see a man who looks exactly like him out walking the streets with his dog. When Jim also reports a similar sighting of his double, Des realises that the duplicate must be an evil alien bodysnatcher sent to steal his identity and take over his life. Taking another swig of his father-in-law's tonic, Des astrally transfers himself aboard Miss Griffin's spaceship, where the beautiful extraterrestrial warns him to be on his guard; it seems that Des has indeed become the target of an alien duplicate, and the creature will stop at nothing to complete its mission. Under Miss Griffin's instructions, Des uses the power of a potted plant to construct an early-warning device, but after a night lying awake in fear, he decides he has had enough. Steeling himself for a dangerous confrontation, Des sets off with Jim and Cuddly to track down the duplicate and put an end to its evil plan…