Clara and the Doctor are still running from Simeon's creatures, up and up through a ruined TARDIS. Clara begins to feel woozy, a feeling of having done this before -- running through a TARDIS, again and again. The Doctor comforts her by not, telling her that the ship's telepathic circuits are awakening memories that she isn't even supposed to have. She's understandably frantic: "How can I die? What do you mean I died?"
Meanwhile, Simeon needs to open a door and the key is a word and the word is the Doctor's. Who arrives! (People are always arriving like that, with exclamations attached.) Simeon orders him to open the tomb, to answer the question that only he knows: "Doctor, what is your name?" The Doctor is having none of it, so Simeon threatens to kill his friends -- a reliably effective tactic, and more useful here because Simeon's goons reform when attacked.
Before any of that terribleness happens, though, the tomb opens. Out walks River Song. The TARDIS can still hear her (she and the TARDIS are so close). But why did she say his name? Clara is shaken from the attack and gets a conciliatory hug while TGI is happy to have access, finally. It will bring peace for him -- and pain, "everlasting," for the Doctor.
Inside, we see the tomb is actually the main room of the TARDIS. Except the room is all overgrown and glowing a turquoise-blue -- the source of which is a giant arc of energy at the center. "What were you expecting: a body?" the Doctor asks. "Bodies are boring. I've had loads of 'em. That's not what my tomb is for."
No, the tomb holds everything the Doctor's body isn't: "Time travel, it's like a tear in the fabric of reality. This is the scar tissue," he explains, a collection of all of the Doctor's days, good and bad, even the ones he hasn't lived. But being so close to it has weakened him and he collapses. The paradox of his presence is very bad for his health.
TGI approaches the energy -- it's like an open wound and so can be entered. It will kill him as a result, but it will destroy the Doctor by allowing TGI to rewrite his every living moment, turning victories into defeats and poisoning friendships. TGI may be "scattered along his timeline like confetti" but the Doctor will be undone. He enters the stream; the white-skinned men disappear and everyone freaks out.
NEXT: "There will be consequences"