Applause broke the silence, three sharp claps.
"Magnificent spellwork, Tom." Dumbledore looked genuinely impressed. "Your ice magic is without question the finest in the wizarding world."
"I know," Tom said.
It was not arrogance so much as arithmetic. With the Frost Crown's circuits and the notes behind them, producing anything less than the best would have been the embarrassing outcome. Though it was worth noting, even if only to himself, that raw magical power had never been a reliable measure of a wizard's worth.
"Teach me sometime," Sirius said, with complete sincerity. "I have money."
Tom liked that about him. No preamble, no hesitation. "Done. I'll sell you a set of notes. Nine thousand, nine hundred and ninety-eight Galleons. You can pass them to Harry, his children, whoever you like."
Dumbledore had watched this exchange from beginning to end. "Tom," he said, "are you in some kind of financial difficulty?"
Nicolas answered for him, amused. "Leave him alone. The boy just enjoys it. It's a hobby. The interest is in the earning, not the having."
"A hobby is important," Sirius said, with feeling. "Harry's at school, I'm at home with nothing to do, no idea what I want, no idea what I'm supposed to be doing with myself."
"Something to think about when we get back," Tom said, already climbing up onto the carriage. He looked back at the group still standing on the cliff. "You're not all planning to walk across the ice, are you? Don't blame me if someone goes through."
They boarded.
The winged horses lifted into the dark and came down at the face of the crack in the cliff. Everyone stepped off, and Dumbledore raised his wand and shaped a set of stone steps leading down into the gap.
Inside, it was completely dark. The floor was wet, scattered with small fish and shellfish dragged in by the tide, plump and glistening in the wandlight.
"Lumos Maxima!"
Sirius thrust his wand forward and light flooded ahead of them, pushing back the dark for twenty feet before it faded into nothing. The stone walls were black and slick, the passage extending further than the light reached.
"Where's the entrance to the cave?" Sirius muttered, turning slowly. "Kreacher said there was a cave."
Kreacher's memory beyond the events involving Regulus had largely collapsed. He could point to approximately the right location, but the specific mechanism for entering the cave was gone. They would have to work it out themselves.
Lupin said nothing. He watched Dumbledore, Nicolas, and Tom all move toward the same wall at almost exactly the same moment, spreading out to cover three different sections of the rock face, hands moving across the stone.
"Here," Nicolas said.
The other two crossed to him immediately, examined the spot for a moment, and both nodded.
"That's it."
Lupin and Sirius exchanged a look. A shared, wordless deflation.
What exactly were they here for?
Sirius, determined to contribute something, held his wand up close to give the three men better light to work by.
Nicolas produced his own wand and pressed the tip against the stone. Gold light spread into the rock face and sank through it, and slowly, on the smooth black surface, the ghost of an arch appeared, with the suggestion of a passage behind it.
"A blood price," Dumbledore said, reading the enchantment with something close to contempt. "Sacrifice to enter. Of course. Voldemort's signature is all over this, the insecurity bleeding through every layer."
"How do we get through?" Sirius asked.
"Blood. A meaningful quantity. Voldemort designed this to weaken whoever came investigating. He clearly didn't trust his own defences to do the job on their own."
"But he never imagined this many of us showing up." Sirius was already transfiguring a stone from the ground into a short blade. "Let me do it. I can't just stand here watching everyone else work while Regulus is in there."
He had the knife raised when Newt spoke.
"Wait."
Everyone looked at him.
"It just needs to be blood, correct?" Newt said, with the perfectly reasonable tone of a man who has not noticed that he has said something that rearranges the entire situation. "Why does it have to be ours?"
Sirius's hand stopped.
The group went quiet for a moment. The atmosphere had been building to something, and Newt had walked straight through it without registering it was there. But then, if Newt had been the sort of person who noticed that kind of thing, he wouldn't have been Newt.
He set his case on the ground and looked up at Dumbledore with the expression of a man indicating that he had considerable inventory to draw from.
The creatures in that case were not uniformly well-behaved. Disputes broke out with some regularity, and over the years Newt had developed the habit of collecting the resulting blood for use in potions work. He was, in practical terms, a mobile blood bank.
Dumbledore was very glad he had brought Newt tonight. He had a strong preference for not watching anyone bleed on his account. Magical creatures, on the other hand, presented no such difficulty.
"What do you need? Dragon blood? Something large?"
"Dragon blood would be ideal. Preferably a single species, that's the safest configuration."
"Dragon blood it is."
Newt sent a Niffler into the case. Five minutes later the Niffler came back out carrying a glass vial, its belly visibly rounder than when it had gone in, clinking faintly with each step.
Newt noticed. He took the vial, tucked the Niffler back into his breast pocket, and decided that particular conversation could wait.
Dumbledore guided the blood against the stone wall in a steady stream. The rock absorbed it without a trace, drinking it down, and when roughly half the vial was gone, the arch solidified. Not the faint outline Nicolas had drawn out of it before, but a real opening in the stone, with a passage beyond.