Star Trek: Season 2, Episode 4

2 - 4: Mirror, Mirror

The Halkans are a people deeply committed to peace. Kirk is trying to negotiate with them for dilithium, the rare mineral that's needed for warp power systems. But if there is even a chance their crystals will be used for violence, they cannot agree. Kirk beams back to his ship as a magnetic storm approaches - but the ship where he materializes is vastly different, run by savage opportunists, sadists, and killers. This ship, part of an Empire, will wipe the Halkans from their world and seize their crystals. Kirk must find a way to prevent that, and to return himself and his landing party home.