“Turn Left” (written by Russell T. Davies) shows just how important Doctor Who has been in Earth’s time line. We get to see just what would have happened if Donna never met the Doctor in Runaway Bride.
This episode also has the much anticipated return of Billie Piper as Rose.
If you haven’t seen the episode, fair warning: here be spoilers.
Bad Wolf hasn’t been present that much in Doctor Who since Season 2. In the Season 1 finale, Rose scatters Bad Wolf references throughout throughout time — and not all of the instances would have been discovered. The Bad Wolf references appear only when Rose is in the series. In that respect, it makes sense that you could have the Bad Wolf references.
Some of the fanfiction stories assume that there is always a residual link to the Time Vortex inside Rose. It’s blocked because of the Doctor’s actions in the Season 1 finale. (Possibly supported by the werewolf character in Season 2 telling Rose that she has “a bit of the wolf” in her.)
The huge display of Bad Wolf at the end of the episode plus the Doctor saying cryptically that the phrase means the end of the world does make you wonder… There were rumours on some of the episode summaries (see Sylvester McCoy’s Doctor Who page) that the last episodes for this season would delve into the Time Wars. There were also rumours that the last episodes of this season would undo most of the cannon established by Russell Davies (which would mean the Time Wars would have to be undone to bring back Gallifrey).
Did you notice the footage of Davros in the DW Confidential footage? He isn’t named, but it’s hard to miss that critter’s chair and head-gear even in the shadows.