Yeah, it's River Song. She takes off her glasses and winks at the camera, even as the Doctor is stealing the Homebox away from the Archive. I like the actress, so the smugness doesn't bother me. And of course, given their Mel Bush history together, you have to look at everything she's said before when she shows up again: In her lifetime they've visited the Bone Meadows and Asgard, for a picnic, and the "wreck of the Byzantium," which is what this story is about. We're in the middle of the story, since he's met her and she's met him, two beginnings, and we know when she dies, which is the ending. So we know that's not today. We know when Tuxedo says, "Party's over, Doctor Song," that it's not really over.
The Doctor plugs the Homebox into an old TARDIS screen, and they watch River get cornered. She explains to Tuxedo that she needed to see what was in the Starliner's vault. "Do you all know what's down there? Any of you? Because I'll tell you something. This ship won't reach its destination." Tuxedo orders her death, and she grins up into the cameras again. "7775/349x10-0-12/acorn. Oh, and I could do with an air corridor." And if you're listening then you already know how friggin' awesome it's about to get.
River tells Tuxedo he might want to grab onto something -- "like I said on the dance floor," the little minx -- and then blasts her way off the Starliner, and into space, blowing a kiss, arms thrown wide like the Green Fairy. That is bad-ass. None of this "Basically, I rule" shit: Just a blown kiss and a blown airlock, and then before you know it she's danced across the firmament, and into his arms.
They give chase to the Byzantium, and within seconds she's started that River Song shit, teaching the Doctor how to drive the TARDIS better than he ever could. "Use the stabilizers. The blue switches!" He swears they don't do anything, and she applies them; the TARDIS evens out immediately. The Doctor pretends this is a hindrance, that he likes it when things are bumpy: "Yeah, well, it's just boring now, isn't it? They're boringers. They're blue boringers." (Remind me to pay attention to whether he keeps using them -- it would be excellent if he did from now on, but I always forget to listen to the TARDIS; even the Cloister Bell has to be pointed out to me.)
River Song immediately does six impossible things with the TARDIS, locking onto the ship they're following and parking the TARDIS alongside. "Parked us? We haven't landed!" They have. "It didn't make the noise!" What noise? River explains that it's not supposed to make the noise, that he just drives with the brakes on. He digs his heels in: "Yeah, well, it's a brilliant noise. I love that noise."