Out on the stone steps, Harry turned to the others. "Right, here's what we've got to do," he whispered urgently. "One of us has got to keep an eye on Snape — wait outside the staff room and follow him if he leaves it. Hermione, you'd better do that."

"Why me?"

"It's obvious," said Ron. "You can pretend to be waiting for Professor Flitwick, you know." He put on a high voice, "'Oh Professor Flitwick, I'm so worried, I think I got question fourteen b wrong....'"

"Oh, shut up," said Hermione, but she agreed to go and watch out for Snape.

"And we'd better stay outside the third-floor corridor," Harry told Ron. "Come on."

But that part of the plan didn't work. No sooner had they reached the door separating Fluffy from the rest of the school than Professor McGonagall turned up again and this time, she lost her temper.

"I suppose you think you're harder to get past than a pack of enchantments!" she stormed. "Enough of this nonsense! If I hear you 've come anywhere near here again, I'll take another fifty points from Gryffindor! Yes, Weasley, from my own house!"

Harry and Ron went back to the common room, Harry had just said, "At least Hermione's on Snape's tail," when the portrait of the Fat Lady swung open and Hermione came in.