Dumbledore came through the door of number twelve Grimmauld Place with snow still on his robes, having moved fast enough from Hogwarts that he had not stopped to shake it off.
"Good evening, gentlemen." He nodded to both of them, and then his gaze settled on Sirius, whose state was apparent without needing to be described.
"Would someone like to tell me what has happened?"
Tom showed no inclination to start, so Sirius told it himself, his voice rougher than usual, going through Regulus's story for Dumbledore and for Phineas, who had reappeared in his frame somewhere during the telling.
Dumbledore's face moved through several things as he listened. When Sirius finished, the old man looked at the locket, at what Regulus had traded his life to retrieve. Phineas sat very still in his frame, lips pressed together so tightly they had gone thin.
Then he laughed, short and cold.
"The pair of you should have been sorted into Gryffindor, clearly. One dies to save a house-elf from a basin of poison. The other wants to run headlong into the same trap to recover a corpse." He let the silence do some work. "That is not a clever serpent. That is a very stupid lion."
He turned and left the frame before Sirius could get a word out.
"He was a hero." Dumbledore's voice was quiet but carried weight. "Regulus showed through his choices and his death what he truly understood about nobility and blood. He was every inch a Black."
"Professor." Sirius's voice dropped. "Please. Help me bring Regulus home."
"It would be my honour." Dumbledore said it without any performance. "I am ready to leave whenever you are. And Tom..."
"I'm coming," Tom said, before Dumbledore could finish the sentence.
Dumbledore frowned. "Tom, I have complete confidence in your abilities, but there is genuinely no need for you to"
"Tom," Sirius added, "stay here, read your books, we'll be back before you know it, Dumbledore and I can handle"
Tom shook his head. "I'm not coming to watch. I have a reason."
"Which is?" Sirius asked, without quite thinking.
"Inferi." Tom crossed to Dumbledore and held out the locket, letting the old man take it. "I need a large supply of Inferi for research. Nicolas knows about this already. I'm planning to bring him along."
The truth was that Tom admired what Regulus had done in abstract terms, the clarity of mind required to swap a Horcrux for a convincing fake and drink whatever Voldemort had put in that basin. But Tom was not in the habit of involving himself in other people's problems out of sentiment. The Horcrux was already in hand. The cave itself had become optional.
What was not optional was the lake full of Inferi.
Inferi were former humans, caught in the space between life and death, and Dark wizards had used them for centuries as guardians of valuables and burial sites. What interested Tom was something more specific: whether the residual consciousness and spiritual essence from their former lives could be extracted. His alchemical creature creation had reached a point where the techniques were largely sound. The missing component was raw material of exactly this kind.
"Nicolas Flamel..." Sirius worked through it slowly. "The one who made the Philosopher's Stone? Six hundred years old? But didn't he-"
"That was a cover story. To stop a steady stream of people coming after the Stone, the way Voldemort did two years ago."
"Right." Sirius filed this away. He knew the name from Harry's account of his first year. Without that, he would not have given Nicolas Flamel a second thought in his life.
"Dumbledore, what do you think?" He looked toward the old man.
Sirius wanted Nicolas there. A wizard who had been alive for six hundred years represented a category of experience that was simply unavailable elsewhere, and for something like this, experience was worth more than almost anything.
Dumbledore agreed. When dealing with Voldemort's constructions, the more combined knowledge brought to bear on the problem, the better. Nicolas Flamel's reputation alone would shape how the situation was read by anyone who heard about it afterward. Tom at fifteen was formidable. Nicolas at six centuries was a different kind of authority entirely, and no one was going to question his judgment.
"Very well. Sirius, can you wait one more day? Tom, would you let Nicolas know? If possible, tomorrow night at midnight, back here."
Tom nodded and left Grimmauld Place.
Throughout all of it, Dumbledore had not once asked Tom how he had known about Regulus. There were people he would have pressed on that question without hesitation. Tom was not one of them. Ability and potential earned a particular kind of respect from Dumbledore, and that respect included not asking questions the other person had already decided not to answer.
Whatever side Tom was on, it was not Voldemort's. For now, that was enough.
...
The following morning, Tom found Nicolas in the house where he had been staying and told him everything.
"Extracting spiritual essence from Inferi?"
Nicolas listened to the full idea and could not quite suppress his admiration for the sheer inventiveness of it, though he paired the admiration with honest scepticism. "Are you certain any spiritual essence would have survived the transformation? And even assuming it has, are you certain that essence, having been steeped in Dark magic, wouldn't compromise the alchemical creature it goes into?"
"If I already knew the answers, it wouldn't be an experiment."
"Fair point." Nicolas nodded. "Then let's go and see." He paused. "Actually, bring Newton as well. Strictly speaking, Inferi do fall under the category of magical creatures."
...