Very excitedly, the Doctor and Rose go check out the futility on the monitors, and his grin falls like it was meant to, and she asks a meaningless question as his head drops to his knees. The Doctor gives her a lie in response, because he loves her. But Rose know something is up: "Is that bad? How bad is it?" And oh, the perky spark in his eyes, bright like a fever, as he jumps up, to anyone's eyes overjoyed. "Rose Tyler, you're a genius!" He plants a kiss on her head, but it's a shadow, an echo, a lie: "We can do it! If I use the TARDIS to cross my old timeline.... Yes!"
The Doctor fires himself toward the TARDIS. Rose follows close behind. If he just keeps talking he won't have to say anything; he won't betray himself. Remember Pete Tyler's apartment? How she just kept talking? "Hold that down, and keep position!" the Doctor shouts, excited, pointing at a level, ignoring Rose's questions. She holds it down, unknowingly canceling the forcefield, giving the TARDIS a way out. The Doctor: "If I'm very clever -- and I'm more than clever, I'm brilliant -- I might just save the world. Or rip it apart." She says that she'd go for the first one, cutely, and he agrees: "Now, I've just got to go and power up the Gamestation. Hold on!" He runs out again, so happy and full of energy that you know the Daleks are screwed. And the TARDIS door shuts behind him, and his face goes cold, and he stops running, and turns around.
Inside the TARDIS, Rose waits for him, equally excited, loving this part. The Doctor raises his screwdriver and points it at the TARDIS. And the engines start to run. "Doctor, what're you doing?" Rose shouts from inside. "Can I take my hand off? It's moving!" And outside, the Doctor keeps the screwdriver steady. Rose panics and tosses herself at the doors. He's always leaving, and it always hurts, no matter how many times it happens. Ask Jack in an hour. Rose: "Doctor, let me out! Doctor, what have you done?" And the TARDIS fades away, and the Doctor's alone. It's been bad before, when they've been separated, but at least when Rose died he could cry about it. This time it was his idea.
Rose pounds on the door as the TARDIS hurtles through the time vortex, which is blue-shifting: the Doctor is sending her back to Jackie, and Harrod's, and chips. All the things he loves about her, that he could never have. He's sending her home. Then things get wicked sad. (I think we lost some of this, too.) "This is Emergency Program One," says the Doctor. Rose spins around and sees a hologram of the Doctor. There are some neat production things going on here: he's shaky and technical-looking, and his voice is kind of sciencey. "Rose, now listen; this is important. If this message is activated, then it can only mean one thing: we must be in danger, and I mean fatal. I'm dead, or about to die any second, with no chance of escape." Rose jumps forward, screaming protest. And the Doctor hologram continues: "And that's okay. Hope it's a good death." And Rose stops and stares up at him, on the ramp to the console. The Doctor: "But I promised to look after you, and that's what I'm doing. The TARDIS is taking you home." She rushes toward him, promising that this isn't going to happen: "I won't let you." The hologram speaks into space: "And I bet you're fussing and moaning now. Typical. But hold on and just listen a bit more. The TARDIS can never return for me. Emergency Program One means I'm facing an enemy that should never get their hands on this machine. So this is what you should do: let the TARDIS die." The last time Rose and the Doctor separated, that's practically what happened. The keys went useless. The Doctor's hologram continues to speak: "Just let this old box gather dust. No one can open it, no one will even notice it. Let it become a strange little thing standing on a street corner. And over the years, the world will move on and the box will be buried." Heaven on a street corner. After all that. I'm telling you, I lost it. "And if you wanna remember me, then you can do one thing, that's all. One thing." And he turns to us/her, beautiful, lit up. Voice clear now, not like a hologram or anything. Just the Doctor. Eyes full, and focused. Like he knows that she's there. Like he knows that we're there. "Have a good life," he says. "Do that for me, Rose. Have a fantastic life." Stories about grace don't mean anything until it touches you. It's a tall order he just issued. And the only one that means anything.