WHO: Rose & Nine WHERE: Karn (except in this world, it's called... um... Yarn. Who cares.) WHEN: Tonight (in a Timey-Wimey sense) WHAT: A New Beginning WARNINGS: Absolutely no idea.
Eleven had given the Doctor another place to check into in his hunt to extend Rose's life and, if he was lucky, grant her regeneration. She'd already spent more time in the Time Vortex than most, and from what he understood that alone had changed some of the other companions. Add in the Bad Wolf incident, and her changed DNA, he felt like he had all the pieces to the puzzle and just was failing to make them fit.
And, clever as he was, this hadn't changed.
He landed the TARDIS on the world of Karn, or whatever they called it here. Rather than leaving Rose behind the Doctor had taken her along, knowing full well if he kept trying to coddle her she'd likely get quite cross with him.
"Karn wasn't somewhere we could visit in the old universe," The Doctor said to Rose, spinning a wheel and turning a lever. "It was behind the time lock."