Dumbledore had already crossed the crenellated ramparts and was dismounting; Harry landed next to him seconds later and looked around.
The ramparts were deserted. The door to the spiral staircase that led back into the castle was closed. There was no sign of a struggle, of a fight to the death, of a body.
“What does it mean?” Harry asked Dumbledore, looking up at the green skull with its serpent’s tongue glinting evilly above them. “Is it the real Mark? Has someone definitely been—Professor?”
In the dim green glow from the Mark Harry saw Dumbledore clutching at his chest with his blackened hand.
“Go and wake Severus,” said Dumbledore faintly but clearly. “Tell him what has happened and bring him to me. Do nothing else, speak to nobody else and do not remove your Cloak. I shall wait here.”
“But—”
“You swore to obey me, Harry—go!”
Harry hurried over to the door leading to the spiral staircase, but his hand had only just closed upon the iron ring of the door when he heard running footsteps on the other side. He looked round at Dumbledore, who gestured to him to retreat. Harry backed away, drawing his wand as he did so.
The door burst open and somebody erupted through it and shouted: “Expelliarmus!”
Harry’s body became instantly rigid and immobile, and he felt himself fall back against the Tower wall, propped like an unsteady statue, unable to move or speak. He could not understand how it had happened—Expelliarmus was not a Freezing Charm—
Then, by the light of the Mark, he saw Dumbledore’s wand flying in an arc over the edge of the ramparts and understood… Dumbledore had wordlessly immobilised Harry, and the second he had taken to perform the spell had cost him the chance of defending himself.
Standing against the ramparts, very white in the face, Dumbledore still showed no sign of panic or distress. He merely looked across at his disarmer and said, “Good evening, Draco.”
Malfoy stepped forwards, glancing around quickly to check that he and Dumbledore were alone. His eyes fell upon the second broom.
“Who else is here?”
“A question I might ask you. Or are you acting alone?”