Quirrell snapped his fingers. Ropes sprang out of thin air and wrapped themselves tightly around Harry.

"You're too nosy to live, Potter. Scurrying around the school on Halloween like that, for all I knew you'd seen me coming to look at what was guarding the Stone."

"You let the troll in?"

"Certainly. I have a special gift with trolls — you must have seen what I did to the one in the chamber back there? Unfortunately, while everyone else was running around looking for it, Snape, who already suspected me, went straight to the third floor to head me off — and not only did my troll fail to beat you to death, that three-headed dog didn't even manage to bite Snape's leg off properly.

"Now, wait quietly, Potter. I need to examine this interesting mirror.

It was only then that Harry realized what was standing behind Quirrell. It was the Mirror of Erised.

"This mirror is the key to finding the Stone," Quirrell murmured, tapping his way around the frame. "Trust Dumbledore to come up with something like this... but he's in London... I'll be far away by the time he gets back...."

All Harry could think of doing was to keep Quirrell talking and stop him from concentrating on the mirror.

"I saw you and Snape in the forest —" he blurted out.

"Yes," said Quirrell idly, walking around the mirror to look at the back. "He was on to me by that time, trying to find out how far I'd got. He suspected me all along. Tried to frighten me - as though he could, when I had Lord Voldemort on my side...."

Quirrell came back out from behind the mirror and stared hungrily into it.

"I see the Stone... I'm presenting it to my master... but where is it?"