Commander Kritakh and his second Torlakh are two Zygons that have been trapped on Earth for the past 20 years. During that period the two have had plenty of time to recreate their own world here on Earth. The trouble is that Kritakh, in the guise of engineer Mike Kirkwood, has lost his sense of purpose. Can his second Torlakh, in the guise of mass-murderer Bob Calhoun, get his Commander back on track? Just to complicate matters further enter sexy psychiatrist Dr Lauren Anderson. First she is tempted by her innermost desires and then must face her greatest challenge.