 A Martian spacecraft crash-lands near the observatory of Cyrus Layton, designer of Earth s first spaceship. The survivor, forerunner of an invasion, can assume the form of any earthman. Calling himself the "purple monster," the humanoid invader sets about gaining control of Layton s rocket project. Opposing him is Craig Foster, former Secret Service man, who episode by episode tries to thwart the monster s attempts to acquire rocket components. Will Craig ever suspect that his closest associate is really the monster?