At the foot of the first set of stairs, they spotted Mrs. Norris skulking near the top.

"Oh, let's kick her, just this once," Ron whispered in Harry's ear, but Harry shook his head. As they climbed carefully around her, Mrs. Norris turned her lamplike eyes on them, but didn't do anything.

They didn't meet anyone else until they reached the staircase up to the third floor. Peeves was bobbing halfway up, loosening the carpet so that people would trip.

"Who's there?" he said suddenly as they climbed toward him. He narrowed his wicked black eyes. "Know you're there, even if I can't see you. Are you ghoulie or ghostie or wee student beastie?"

He rose up in the air and floated there, squinting at them.

"Should call Filch, I should, if something's a-creeping around unseen."

Harry had a sudden idea.

"Peeves," he said, in a hoarse whisper, "the Bloody Baron has his own reasons for being invisible."

Peeves almost fell out of the air in shock. He caught himself in time and hovered about a foot off the stairs.

"So sorry, your bloodiness, Mr. Baron, Sir," he said greasily. "My mistake, my mistake — I didn't see you — of course I didn't, you're invisible — forgive old Peevsie his little joke, sir."

"I have business here, Peeves," croaked Harry. "Stay away from this place tonight."

"I will, sir, I most certainly will," said Peeves, rising up in the air again. "Hope your business goes well, Baron, I'll not bother you."

And he scooted off "Brilliant, Harry!" whispered Ron.

A few seconds later, they were there, outside the third-floor corridor — and the door was already ajar.