Kirk beams back to the planet with Lazarus and a security team to seek this enemy. Lazarus has another dimensional corridor episode and is returned to sickbay. Lazarus explains to Kirk that he is a time traveler; the planet below was once his home world. Lazarus claims his enemy destroyed his civilization in the past, for which Lazarus has chased him for centuries. Mr. Spock develops a hypothesis that Lazarus's enemy is his counterpart from an anti-matter universe. If he and his anti-self contact each other within either physical universe outside the dimensional corridor, they would annihilate both the matter and anti-matter universes.