The Stargate crew (including Captain O’Neill, of course) have tracked down the last of the clones of the infamous Goa’uld System Lords and are ready to kill him off to make the many universes safe, but in his last words, he reveals the original Lord still lives. Indeed, he does! And he has traveled back to 1939 to sink the ship that was bringing the artifact that created the Stargate program in the first place. Even though his plan doesn’t fully succeed, various crew in the present start disappearing while others end up back in 1939 where they are rescued by a Stargateless Captain O’Neill from the future.

That’s just for starters. Yet to come are changes to the past and subsequent changes to change those changes back, all with no sensible model of time travel.