K-9, still shooting, worries that his power supply is failing. Finch Josses at his brothers to "forget the shooty dog thing," and K-9 finally reaches the end of his power supply, and goes to sleep.
The Doctor and Companions end up back in the Physics lab. "It's the oil," he suddenly exclaims. "Krillitane life forms can't handle the oil! That's it! They've changed the physiology so often, even their own oil is toxic to them." (They've forgotten where they came from, and who they are. They've forgotten what they are. They've changed too much, traveled too far from their daylight selves. They've become used to the skins they wear and forgotten what lies beneath them: they are auto-toxic. It's what happens.) "How much was there in the kitchens?" Barrels. The Krillitanes rip holes through the classroom door with their claws. The Doctor orders everybody to run some more, this time to the kitchens; he turns to Mickey -- "What now, hold the coats?" -- and tells him to get the kids unplugged and outside the school. "Now then. Bats, bats, bats. How do we fight bats?" Kenny, without speaking, breaks the glass of a fire alarm with his elbow and sets it off. Oh, I like him! The Krillitanes wince and scream at the sound; the Doctor practically throws some kisses Kenny's way. Out in the hallway, they just run past the Krillitanes, who are in no mood. Finch grits his teeth and punches through a wall to the wiring inside, cutting off the alarm. (No screwdriver for him, but again: the wires behind things that power the way they control you, just like with the computers before.) Finch orders the Krillitanes after the gang and heads down.