The logic goes like this:
"The Vampire Diaries" will now premiere on Thursday, October 3, one week earlier than previously announced. "The Originals," which of course spun off from "The Vampire Diaries," will get a one-week showcase after the vamp-and-werewolf mothership that night.
"The Originals" will move to its regular time period on Tuesdays at 8 p.m. the following week, on October 8, leading into "Supernatural," which had previously been scheduled to premiere the following week.
The CW had originally planned on holding back on its Tuesday dramas so that "The Originals" could at least be promoted on "The Vampire Diaries," rather than premiering two days before. Instead, everything got a shake-up.
In addition to the one original airing after "The Vampire Diaries," "The Originals" will encore its second episode after the October 10 episode.
This move with push the premiere of the Mary Queen of Scots drama "Reign
" to October 17.