“Professor Snape and I heard noises, Professor,” said Filch at once. “Peeves the Poltergeist, throwing things around as usual—and then Professor Snape discovered that someone had broken into his off—”

“Shut up!” Snape hissed to Filch.

Moody took a step closer to the foot of the stairs. Harry saw Moody’s magical eye travel over Snape, and then, unmistakably, onto himself.

Harry’s heart gave a horrible jolt. Moody could see through Invisibility Cloaks . . . he alone could see the full strangeness of the scene: Snape in his nightshirt, Filch clutching the egg, and he, Harry, trapped in the stairs behind them. Moody’s lopsided gash of a mouth opened in surprise. For a few seconds, he and Harry stared straight into each other’s eyes. Then Moody closed his mouth and turned his blue eye upon Snape again.

“Did I hear that correctly, Snape?” he asked slowly. “Someone broke into your office?”

“It is unimportant,” said Snape coldly.

“On the contrary,” growled Moody, “it is very important. Who’d want to break into your office?”

“A student, I daresay,” said Snape. Harry could see a vein flickering horribly on Snape’s greasy temple. “It has happened before. Potion ingredients have gone missing from my private store cupboard . . . students attempting illicit mixtures, no doubt . . . ”

“Reckon they were after potion ingredients, eh?” said Moody. “Not hiding anything else in your office, are you?”

Harry saw the edge of Snape’s sallow face turn a nasty brick color, the vein in his temple pulsing more rapidly.

“You know I’m hiding nothing, Moody,” he said in a soft and dangerous voice, “as you’ve searched my office pretty thoroughly yourself.”

Moody’s face twisted into a smile. “Auror’s privilege, Snape. Dumbledore told me to keep an eye—”

“Dumbledore happens to trust me,” said Snape through clenched teeth. “I refuse to believe that he gave you orders to search my office!”

“’Course Dumbledore trusts you,” growled Moody. “He’s a trusting man, isn’t he? Believes in second chances. But me—I say there are spots that don’t come off, Snape. Spots that never come off, d’you know what I mean?”

Snape suddenly did something very strange. He seized his left forearm convulsively with his right hand, as though something on it had hurt him.

Moody laughed. “Get back to bed, Snape.”

“You don’t have the authority to send me anywhere!” Snape hissed, letting go of his arm as though angry with himself. “I have as much right to prowl this school after dark as you do!”

“Prowl away,” said Moody, but his voice was full of menace. “I look forward to meeting you in a dark corridor some time . . . You’ve dropped something, by the way . . . ”