"Very well, Severus. I didn't really expect Black to linger." 

"Have you any theory as to how he got in, Professor?" asked Snape. 

Harry raised his head very slightly off his arms to free his other ear, 

"Many, Severus, each of them as unlikely as the next." 

Harry opened his eyes a fraction and squinted up to where they stood; Dumbledore's back was to him, but he could see Percy's face, rapt with attention, and Snape's profile, which looked angry. 

"You remember the conversation we had, Headmaster, just before -- ah -- the start of term?" said Snape, who was barely opening his lips, as though trying to block Percy out of the conversation.

 "I do, Severus," said Dumbledore, and there was something like warning in his voice. 

"It seems -- almost impossible -- that Black could have entered the school without inside help. I did express my concerns whet, you appointed --" 

"I do not believe a single person inside this castle would have helped Black enter it," said Dumbledore, and his tone made it so clear that the subject was closed that Snape didn't reply. "I must go down to the dementors," said Dumbledore. I said I would inform them when our search was complete." 

"Didn't they want to help, sir?" said Percy. 

"Oh yes," said Dumbledore coldly. "But I'm afraid no dementor will cross the threshold of this castle while I am headmaster." 

Percy looked slightly abashed. Dumbledore left the hall, walking quickly and quietly. Snape stood for a moment, watching the headmaster with an expression of deep resentment on his face; then he too left. 

Harry glanced sideways at Ron, Hermione, and Amelia. All of them had their eyes open too, reflecting the starry ceiling.