In a Mirror, Darkly

"In a Mirror, Darkly" is the eighteenth and nineteenth episodes of the fourth season of the American science fiction television series Star Trek: Enterprise, and originally aired on April 22 and 29, 2005. This installment was developed to be a sequel to The Original Series episode "The Tholian Web" and a prequel to "Mirror, Mirror". The decision to set an Enterprise episode in the mirror universe originated with a pitch to enable William Shatner to appear in the series. The teleplays for both parts of the episode were written by Mike Sussman, with Manny Coto contributing the story for the second part.

Set in the 22nd century, the series normally follows the adventures of the first Starfleet starship Enterprise, registration NX-01. However, these installments feature a mirror universe Jonathan Archer and evil counterparts of the normal characters, who serve the cruel and militaristic Terran Empire. In the first part, the ISS Enterprise learns of a Starfleet ship from the future of the main universe which is being stripped for parts by the Tholians, and seeks to take the ship from the aliens. The second part sees the surviving crew operating the USS Defiant and seeking to overthrow the Empire using its advanced weaponry.

The episode saw the reuse of footage from Star Trek: First Contact and the creation of an alternative opening credits sequence which included footage from other Paramount properties such as the film The Hunt for Red October. A three-quarters-around bridge from The Original Series era was constructed, as well as other sets from a Constitution-class starship. A Gorn and a Tholian were both created using CGI, with the Gorn using motion capture techniques. This installment also saw the return of Vaughn Armstrong as Admiral Maxwell Forrest after his main universe character was killed on screen earlier in the season in the episode "The Forge". This episode subsequently appeared in several lists of the best episodes of Star Trek: Enterprise. It was nominated for an Emmy Award for Outstanding Hairstyling for a Series in 2005.