Set in the universe of Star Trek: The Next Generation, a doorway is opened from another universe and the crew of the U.S.S Enterprise must battle their toughest enemy yet?themselves.

One hundred years ago, four crewmembers of the U.S.S EnterpriseTM crossed the dimensional barrier and found a mirror image of their own universe, populated by nightmare duplicates of their shipmates. Barely able to escape with their lives, they returned, thankful that the accident which had brought them there could not be duplicated, or so they thought.

But now the scientists of that empire have found a doorway into our universe. Their plan is to destroy from within, to replace a Federation Starships with one of their own. Their victims are the crew of the U.S.S. Enterprise NCC-1701-D, who now find themselves engaged in combat against the most savage enemies they have ever encountered, themselves.

Diane Duane is the author of The Door Into Fire, which was nominated for the World Science Fiction Society's John W. Campbell Award for best new science fiction/fantasy writer two years in a row. Duane has also published more than thirty novels, numerous short stories, and various comics and computer games, several of which appeared on the New York Times bestseller list. She is best known for her continuing Young Wizards series of young adult fantasy novels about the New York-based teenage wizards Nita Callahan and Kit Rodriguez. The 1983 novel So You Want to Be a Wizard and its six sequels have been published in seven other languages.