Dark Mirror

Know about the book -

Dark Mirror is written by Diane Duane and published by Simon and Schuster. It's available with International Standard Book Number or ISBN identification 1471109445 (ISBN 10) and 9781471109447 (ISBN 13).

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.