"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.