"But he was clever, because every word he said was true. Parseltongue really was a gift, and bloodline really was proof. He hadn't lied. So he wouldn't be held accountable, wouldn't be investigated, and no one would say he'd done anything wrong. That was the most formidable part." He returned the test tube to the rack, his voice so soft it was almost a murmur to himself. "Tell the truth, do evil."
Severus Snape reached out and took the bottle of pale blue liquid from the shelf. The glass was cold, and the surface of the liquid rippled faintly, as though something inside it were breathing. "This is the potion Draco provided?"
Dumbledore nodded. "Professor Sprout analyzed it for two days. Its composition is highly complex, and some of its ingredients don't appear in any known potions texts. It can indeed prevent petrification, but it conceals something else as well."
He took off his glasses, wiped the lenses, and put them back on. "A magical imprint. Nothing obvious—something exceedingly faint, as though it had been diluted countless times... a mark."
Severus Snape put the bottle back on the shelf. "A mark for what? Who is behind it?"
Dumbledore did not answer. He looked at the transparent dome of the Greenhouse, at the treetops of the Forbidden Forest beyond it, lit by the moon and swaying in the wind.
"I only know that whoever is behind this does not intend to control those who drink the potion. He only needs to know where they are. If one day he wishes to do something to them, those marks will be the hands he reaches into the castle with."
Outside the window, moonlight emerged from behind the clouds, turning the treetops of the Forbidden Forest into a silver sea. Under the mingled glow