As the store closes up for the night, the Doctor and Craig start skulking around in search of the cybermat. Alfie comes along via a papoose the Doctor gives Craig. They soon capture the cybermat, which seems kind of cute until it bares its rows of sharp metal teeth. Craig shrieks and has a bit of a freakout. At the same time, the security guard has just been attacked by a Cyberman and lets out an agonized scream. The Doctor bolts and finds him lying unconscious in the basement. The Cyberman knocks the Doctor clean out and the next thing he sees is Craig's worried face staring down at him. The Doctor gets up and stumbles around a bit, confused because the Cybermen shouldn't have been able to use the sonic-fused teleporter. Also, one of its arms was old and rusty. They've been abducting people and turning them into Cybermen with spare parts, but they didn't take the Doctor because he isn't "compatible."
They head back to Craig's place to plan their next move. Craig pops out for some milk, leaving the Doctor to entertain Stormageddon. The baby cries and cries. "Stop crying," the Doctor says with a gentle smile. "You've got a lot to look forward to, you know... Mortgage repayments; the 9-to-5; a persistent, nagging sense of spiritual emptiness..." He got that from Sesame Street. It was that episode with "X is for Xanax!" He sonics the kid's lamp to make it reflect a panoply of stars on the ceiling. He waxes nostalgic about walking among the stars and hopes Alfie has as much fun as he did. It's pretty sad, actually. Hopefully Alfie doesn't speak Adult or he'll be a basket case before he's even walking. By then, the cybermat has come back to life and tracked the Doctor down. It gnashes its teeth at him. He runs with Alfie out of the house, dropping his screwdriver and locking himself out in the process.
Craig returns home and is attacked by the cybermat. The Doctor stashes Alfie in a swing, then crashes through a glass door to Craig's rescue. Danger and hilarity ensue! They take turns wrestling with this tiny metallic thing until the Doctor finally sonics it with the right frequency. The Doctor congratulates Craig, who also looks quite pleased with himself. Later, they all have a sit-down in the living room while the Doctor reprograms the cybermat's brain and tries to figure out why the Cybermen need it to harvest power for them. "Do you still feel safe with me?" the Doctor asks. He calls himself a "stupid, selfish man" and blames himself for putting people in danger. Craig sensibly tells him not to blame himself. "If it weren't for you, this whole planet would be in absolute ruin." But the Doctor is feeling morose, what with his impending death and all. He confesses that he'll die tomorrow. "I can't put it off anymore," he says. "Tomorrow" seems like a fluid thing to a time traveler. Couldn't you flit about the universe for a thousand years and still make it on time? But Craig, exhausted, has fallen asleep with Alfie on his chest. The Doctor tenderly covers them both with a blankie.