Star Trek Viewing Guide
Chapter 3 · The Expanding Federation
  1. 1The Road to the Federation2063–2161
  2. 2Toward the Five-Year Mission2230s–2261
  3. 3The Expanding Federation2265–2268
  4. 4The Long Road to Khitomer2268–2293
  5. 5A New Generation2324–2367
  6. 6Continuing Voyages2367–2369
  7. 7New Frontiers and Foundations2369–2370
  8. 8Exploring New Quadrants2371–2372
  9. 9Storms on the Horizon2372–2373
  10. 10The Dominion War2373–2375
  11. 11Trying to Get Home2375–2379
  12. 12Life on the Lower Decks2380–2382
  13. 13Echoes and Legacies2383–2401
  14. 14The Far Future3074–42nd century

The Original Series · S1 · E28

The Alternative Factor

First aired March 29, 1967

An alien being fights himself across two realities.

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