Rose calls to Captain Jack -- "Well? Hurry up then!" -- and he jumps up, dashing inside. Rose is there, teaching the Doctor new moves, mumbling encouragement. Jack's astounded at the size of the TARDIS inside as they twist, showing him their story. Rose: "Right, and turn..." The Doctor twists her around awkwardly. "Okay, okay," she says. "Try and spin me again, but this time don't get my arm up my back! No extra points for a half-nelson." The Doctor looks at her, put out, and swears that he used to be able to do this -- a globeful of anoraks clasp hands over their ears. The Doctor tells Jack to shut the door: "Your ship's about to blow up. There's gonna be a draft." Rose sighs and leans against a pillar as the Doctor starts up the TARDIS engines. "Welcome to the TARDIS," he says, but Captain Jack's not equipped to understand what he's really saying, which is, "Welcome to the TARDIS." Everybody lives. "...much bigger on the inside..." Jack whispers, and the Doctor turns to him: "You'd better be." Rose grins and takes Jack's hand: "I think what the Doctor's trying to say is...you may cut in." (As I write this paragraph, this song comes on shuffle. I don't make up the news, I just report it.)
It shakes something loose: if Rose is teaching the Doctor how to be alive in the face of horror, if she's his Wendy, then that makes Jack...somebody who needs to be there more than the Doctor needs him to be there. Surrogate mothers everywhere: a pride. The need to protect, against the crush of the dark, is something natural: one more thing he has in common with Nancy, the mother of all London. But Captain Jack is something else: the barbed-wire fence the Doctor can put between himself and Rose. Captain Jack might act like Pete Tyler, but you could call him "Jacks" too. Suddenly, the Doctor exclaims, "Rose! I've just remembered!" Lights begin to flash, "In The Mood" begins to play, and the Doctor remembers that he can dance. It's a perfect song for dancing, especially here, in context. "In The Mood." How weird is this gonna get? Rose offers her thought that Captain Jack might like this dance, and the Doctor winks and gives a flourish: "I'm sure he would, Rose. I'm absolutely certain. ...But who with?" Captain Jack clears his throat, and Rose hops up onto the steps. Jack watches them, these two, smiling hugely, dancing in perfect step. The Doctor throws Rose over his arm, and she squeals with joy, and the Captain looks away, still smiling. Rose pulls herself up and collapses onto the Doctor's shoulder, giggling. And Captain Jack smiles on them both.