In a recapitulation of the series' cliffhanger, ''Alien Nation: Dark Horizon'' begins with Susan Francisco and her daughter Emily falling victim to a newly developed viral infection that was created by a group of human Purists to exterminate the Tenctonese species. There is also a new sub-plot running parallel to this one, the story of Ahpossno, a Tenctonese Overseer who lands on Earth to find any surviving Tenctonese and bring them back into slavery. The idea of a signal sent into space by the surviving Overseers was explored in the ''Alien Nation (TV series)'' episode "Contact".
