Babylon 5: Thirdspace (1998) is a made-for-television film that is part of the Babylon 5 science fiction universe. It was written by J. Michael Straczynski and directed by Jesús Salvador Treviño.
The movie was originally shown on July 19, 1998 on the TNT cable network, during the run of season five (originally being shown between "Movements of Fire and Shadow" and "The Fall of Centauri Prime"). In addition to members of the regular cast of the Babylon 5 TV series, it features the notable guest-stars Shari Belafonte (playing Dr. Elizabeth Trent) and William Sanderson (reprising the role of "Deuce" that he played in the episode "Grail").
According to Straczynski, the film is based on the writings of H. P. Lovecraft (most noticeably, "The Call of Cthulhu"), although Lovecraft's creatures (the Old Ones) are not actually referred to by name in the film.
The action-based story, which ties into the Shadow/Vorlon plotline, centers on the return of an ancient and overwhelming alien force which had once attempted to destroy life in the Milky Way Galaxy.
Read more about Babylon 5: Thirdspace: Plot and Theme, Story Arc Significance and Continuity