Star Trek: 25 Greatest Next Generation Episodes

The first episode of The Next Generation to scratch the surface of time travel involves a duplicate Picard appearing seemingly out of nowhere in a powerless and badly damaged shuttlecraft.

This Picard came from a future where a gigantic sentient rip in the space time continuum destroyed the Enterprise and hurled him back through time in a shuttle that he apparently used to escape... alone. That's always seemed strange, on reflection, considering no ship should go down without her captain...

Regardless, it's a classic episode and one of the best introductions to the show's increasing appetite for time travel and duplicates.