Eventually, George screws up his courage, opens the cupboard and zaps himself into the dollhouse. The dolls pause just long enough for the Doctor to express a modicum of optimism, then start moving toward George. "You created this whole thing," the Doctor tells him. "You can destroy it." George doesn't believe that. The Doctor realizes something is holding the boy back. He remembers George being afraid he was there to take him away. He tells Alex that George's fear of parental rejection was what triggered all this. Alex looks at the boy, who's finally shedding a tear, and fights his way through the dolls to save him. He scoops George up in a big hug. "Whoever you are, whatever you do, you're my son, and I will never, ever send you away." The music swells and light spills out of the cupboard.
Next thing you know, everyone's back at the apartment. Mrs. Rossiter is crawling out of the trash heap. Amy is none the worse for having been miniaturized for the second week in a row. The landlord wakes up hugging his dog. George's mom returns from work to find her boy and husband playing. The Doctor gives her awkward kisses on both cheeks, as is his custom in these situations, and invites her to breakfast. They fill her in, at least as far as saying the Doctor has fixed everything.
When the Doctor leaves, Alex catches up to him. He has some lingering concerns about raising an alien. "He's a Tenza," the Doctor reminds him. "He'll adapt perfectly, be whatever you want him to be." The Doctor says this with a big smile, even though it's a pretty awful notion. Human children can struggle against their parents' expectations, chafe against their destinies, forge their own identities. Not this boy. It's the saddest, creepiest thing about the episode. Or, rather, it would be if it had been anything more than a throwaway line.
The Doctor and the Ponds head back into the TARDIS. As they discuss where/when to go next, a creepy doll voice begins to sing "Tick tock goes the clock, even for the Doctor." The monitor above the console shows the Doctor's date of death, in case the crushing boredom from this episode made you forget.