Inside the TARDIS, the Doctor puts his power cell in place, and the old girl comes to life. The lights shine, the engines hum. The Doctor grins hugely. We've burned off what doesn't work.
Outside, Pete nods at the TARDIS: "So what happens inside that thing, then?" Rose jumps to offer him a tour, but he begs off: "But you two, you know...all that stuff about different worlds. Who are you?" Rose tells him: "Imagine there are different worlds. Parallel worlds. Worlds with another Pete Tyler; Jackie Tyler's still alive. And their daughter..." She trails off, looking up into Pete's eyes, and a lightbulb goes off, and he immediately tries to leave. "I've gotta go --" Rose tries to stop him, offers again to show him the TARDIS, but he shakes his head: "There's all those Lumic factories out there. All those Cybermen still in storage. Someone's got to tell the authorities what happened. Carry on the fight..." The Doctor steps out and calls to Rose. "Only got five minutes of power. We've gotta go." Rose once more offers to have the Doctor show Pete the TARDIS, but he thanks her curtly. The tears come up, and go back down, as Rose stares up at Pete, and her mouth opens, and she says a name: "Dad." Pete begs her to stop, and walks away. Poor guy. As usual, the Doctor rubs the back of his neck nervously, looking at Rose.
The Doctor instructs Jake of Mrs. Moore's real name and family, and tells Jake to notify them: "Tell them how she died saving the world." I like that little moment, a lot. The respect it shows, both inside and outside the show. And the Doctor gets ready to leave, giddy and energized, but Mickey's not moving: "Uh, thing is I'm staying." The Doctor stares, Rose is still freaked out from before, and they both gawp at him. "It sort of balances out," Mickey explains, "Because this world lost its Rickey. But there's me. And there's work to be done with all those Cybermen still out there." Rose tells him again that he can't, but he just shakes his head. "Rose, my gran's here. She's still alive. My old gran. Remember her?" Rose chokes back her tears and nods. "She needs me," says Mickey. Rose wonders about what ifs. Turning back around to look is her sin: "What about me? What if I need you?" Mickey's becoming this: burning off what doesn't work: "Yeah, but Rose. You don't. It's just you and him, isn't it? We had something a long time ago, but...not anymore," he finishes lamely. They both know. Rose promises to come back and visit, stammering and wishing. "We can't," says the Doctor quickly, again. "I told you, travel between parallel worlds is impossible. We only got here by accident. We fell through a crack in time. When we leave, I've got to close it. We can't ever return." With his eyes, he asks again if this is really what Mickey wants; Rose looks stricken and tired. Mickey shakes the Doctor's hand, like a man. Rose gives him her phone, with the code for enlightenment and pain already programmed in. "Get it out there, stop those factories. And good luck, Mickey the Idiot." The Doctor slaps his cheek, touched, and Mickey tells him to watch it. The Doctor takes off into the TARDIS with a grin, leaving Rose and Mickey alone.