One hundred years ago, four crewmembers from the U.S.S EnterpriseTM crossed the dimensional hurdle and found out a mirror picture of their own world, populated by headache duplicates of their shipmates. Barely able to escape with their lives, they returned, thankful how the accident which experienced brought them there could not become duplicated, or so they thought.

But now the researchers of this empire have found a doorway into our world. Their plan is normally to demolish from within, to replace a Federation Starships with among their personal. Their victims are the crew of the U.S.S. Enterprise NCC-1701-D, who now find themselves involved in combat against one of the most savage foes they have ever experienced, themselves.