“Right, but at the wrong time”: City on the Edge of Forever (TOS) vs. Past Tense (DS9)

Kirk and Spock come to some horrible realizations, in a timeless classic; Sisko and Bashir make some disturbing observations, and give us a timely warning.

“You people certainly have interesting problems”: Tomorrow is Yesterday (TOS) vs Future’s End (VOY)

Kirk and Janeway try to preserve the timeline – more or less – when they’re each thrown back to the 20th century.