In an alternate universe, an amoral, imperialistic version of the Enterprise crew, led by Captain Forrest with Archer as his treacherous first officer, makes an astonishing discovery during a mission into enemy alien territory. Meanwhile, a power-hungry Archer schemes against Captain Forrest, his lover Hoshi, and loyal slave T'Pol, so he can lay full claim to the discovery. Later, Phlox happily tortures a captured Tholian for information requested by Archer.

Scott Bakula (Commander Jonathan Archer)
Jolene Blalock (Sub-Commander T'Pol)
John Billingsley (Doctor Phlox)
Linda Park (Ensign Hoshi Sato)
Anthony Montgomery (Sargeant Travis Mayweather)
Dominic Keating (Major Malcolm Reed)
Connor Trinneer (Commander Charles 'Trip' Tucker III)

Vaughn Armstrong (Captain Maxwell Forrest)
Franc Ross (Grizzled Human)
James Cromwell (Zefram Cochrane)
Cully Fredricksen (Vulcan Captain)

• The episode opened with the first contact scene from the end of Star Trek: First Contact. When Zefram Cochrane is supposed to shake the Vulcan captain's hand, he shoots him instead!
  
• The opening credits featured an instrumental theme by Dennis McCarthy, along with images of battles instead of exploration and the Terran Empire logo.
  
• The Original Series 3rd season episode "The Tholian Web" introduced the Tholians and the U.S.S. Defiant.
  
• The mirror Tholians created a rift in the universe and lured a ship into the mirror universe — the U.S.S. Defiant NCC-1764, Constitution-class. The ship is approximately 100 years from the future.
  
• The name on the hull of the mirror NX-01 is I.S.S. Enterprise. The NX-01 registry is gone, replaced by a mirror universe symbol. There are also yellow stripes painted on the top sides of the saucer section.
  
• Mirror Porthos is a rottweiler instead of a cute beagle.
  
• Mirror Mayweather is Archer's bodyguard, not the helmsman.
  
• This episode is the 700th episode of Star Trek produced. (This does not include The Animated Series nor the motion pictures.)
  
• Unlike the other "mirror universe" episodes, this episode (and its conclusion) are entirely contained within the mirror universe. There is no crossing-over (other than the starship Defiant).