In a Mirror, Darkly, Part I & II (Star Trek: Enterprise, Season 4, Episodes 18 and 19)
These two episodes take place in a mirror universe. An evil version of Commander Archer mutinies against Maxwell Forrest, who was captain of the Enterprise in that universe, and the crew goes into Tholian space to capture a Starfleet ship from the future. The events of these episodes are a sequel to "The Tholian Web" from the original series.
Watch Star Trek: Enterprise on CBS All-Access.