Regulus didn't ask his question right away. He glanced at Sirius first.
Sirius was looking at him sideways, eyes angled over without turning his head.
Their gazes met for a split second. Sirius flinched as if burned, snapped his eyes back, and stared at his own knees.
A moment passed. He seemed to decide this looked guilty.
Why should I feel guilty?
His eyes slid back toward Regulus, head still perfectly motionless, gaze drifting from Regulus's face to a painting on the wall, from the painting to the quill on the desk, landing everywhere except where it had been.
Regulus felt secondhand embarrassment watching it.
He looked away and stopped paying attention.
A question was forming. Should Sirius stay? Any discussion would require demonstration.
But on reflection, Spatial Transfiguration wasn't some dark secret. It was advanced Transfiguration, nothing more. If word got out, the worst it proved was that he was good at Transfiguration.
And Sirius wouldn't talk. What would that even look like?
Running to his friends with stories about his brother, waiting for them to comment, mock, or feign indifference?
Too petty. Too cheap. Sirius wouldn't do that.
There was another consideration. Sirius's talent was clear: form and shape.
But Spatial Transfiguration was a different matter entirely. The key was spatial perception, the instinct that space had structure, that it could be touched, the cognitive leap that space could be changed.
Regulus paused on that thought.
Then again, maybe the instinct wasn't strictly necessary. McGonagall was a Transfiguration master, and she could perform spatial transfiguration. Did she have innate spatial perception?
He wasn't sure. Maybe... maybe not.
Perhaps when Transfiguration went deep enough, there was another path to space that didn't require that inborn sense. A path built on understanding Transfiguration itself, pushing the logic of material transformation layer by layer until, pushed far enough, you arrived at space.
But for now, at least for Sirius, and for Regulus himself, the sequence was clear: perceive space first, then change it.
Whether Sirius had that perception, Regulus didn't know.
If he did, all the better. Let this serve as a glimpse of where Transfiguration could go.
If he didn't, he still needed to learn that Transfiguration's reach extended far beyond turning stones into birds.
Regulus set these thoughts aside and looked at McGonagall.
She invited him to state his question directly, neither asking Sirius to leave nor hinting at it.
He understood her intent. Let Sirius watch. Whether it challenged or inspired him, either way it wouldn't hurt.
Fair enough. He asked outright: "Professor, after performing spatial transfiguration, if a spell enters the affected area, the transformation becomes extremely unstable. It collapses on contact. The space either snaps back on its own or the distortion simply vanishes. I'd like to understand why."
McGonagall listened, raised her eyebrows slightly, studied his face an extra beat, then lifted her chin toward the space above the desk, signaling him to demonstrate.
Regulus drew his wand.
The animals were still moving around the office. He waved a hand. The lion vanished, reverting to an eraser. The stag disappeared, a sheet of parchment again. The dog dissolved back into a seat cushion.
Clean. Not even residual magic lingering from the transformations.
Sirius watched his work get undone without reacting. From the moment Regulus had asked that question, he'd gone quiet.
That Regulus hadn't asked him to leave surprised him.
He'd braced himself for it, already prepared to be told to go. But he'd also prepared to stay put as long as McGonagall didn't throw him out.
You got to watch mine. Why shouldn't I watch yours?
Then two words registered. Space and Transfiguration.
Space could be Transfigured?
His mind hadn't finished processing the concept before Regulus began.
Above the desk, the air shivered, a faint distortion, then the region began to change. The boundaries tightened, pulled inward, and the contour of space itself became visible.
Space was deforming, as though someone had gripped a sheet of transparent fabric and twisted, wringing a sharp crease into existence.
The edges of the fold cut clean, light skimming across the surface at a slight angle, bending just enough that the grain of the desk's wood seemed to break at a certain point, a piece of the pattern missing.
Regulus held the distortion steady. His other hand rose, index finger extending toward the fold's edge.
Aguamenti.
Water streamed from his fingertip. Before it reached the crease, the spatial transfiguration collapsed.
The fold snapped flat, yanked taut from both sides, gone in an instant.
Water passed through the space where it had been and splashed across the desk, leaving a small wet stain.
He continued. Space deformed again, the crease reappearing.
A different spell this time. Scourgify. The faint glow touched the boundary of the distortion, and the fold vanished again.
Once more. Disarming Charm. Red light shot from his wand tip, flew toward the fold's edge, didn't quite reach. Space collapsed.
The red bolt punched through the empty space, struck the far wall, and shattered, leaving a shallow scorch mark on stone.
Regulus flicked his left hand. The match on the desk burst into splinters, fine dust scattering through the air.
One fragment drifted upward and transformed mid-flight, body lengthening, wings spreading from its back, legs extending from the abdomen.
A tiny flying insect, wings transparent, legs threadlike, hovering in the air.
It flew forward, reached the edge of the distortion, and the space collapsed.
The insect sailed through the vacated spot, wings still beating, and flew on until it struck the bookshelf and died.
Regulus lowered his wand and looked at McGonagall.
She sat behind her desk, gaze traveling from the spot where the fold had vanished to his face.
A nod of satisfaction came first. "To bring Spatial Transfiguration to this level, Mr. Black, your progress has been rapid."
Then: "How long can you sustain it?"
"Under a minute," he said, inclining his head respectfully.
McGonagall said nothing more. Her gaze shifted to Sirius.
Sirius looked dazed. Mouth slightly open, eyes fixed on the empty air above the desk where the fold had been, mind not yet caught up.
His expression was somewhere between shock and blankness, the look of someone who'd witnessed something that shouldn't exist, the circuit in his brain still trying to connect.
McGonagall turned back to Regulus.
She lifted the teacup from her desk, took a sip, set it down. "Mr. Black, have you considered what makes space fundamentally different from ordinary matter?"
She didn't wait for his answer. "A stone. You Transfigure it into a cup. Once the transformation is complete, the stone doesn't revert on its own. Why? Because the Transfiguration has altered its structure. It isn't permanent, but it won't snap back to its original form the instant you withdraw your magic. Not unless you cast again, or someone breaks the cup. But space is different. You twist it, and it comes back. Why?"
Regulus's mind raced through the question, and a term surfaced: elastic modulus.
Space had elasticity. Its elastic modulus was extraordinarily high, so high that no ordinary material could serve as analogy, possibly without any upper limit at all.
This meant that once space was altered, the restoring force was immense, and constant, pushing back without pause.
The longer the deformation was maintained, the more magic was needed to resist that force. That was why he couldn't hold it for even a minute.
He organized the thought and answered. "After being deformed, space is always trying to snap back. Maintaining the transformation means fighting that restoring force. Anything carrying magic that touches the deformed area introduces a variable into the equilibrium. The balance breaks, and space rebounds."
McGonagall nodded. The lines at the corners of her eyes deepened. "Spatial elasticity. That's a precise way to put it."
Then she asked: "Do you think the elasticity itself can be Transfigured?"
Silence.
What is this?
Elasticity wasn't matter. It wasn't energy. It wasn't anything magic could touch directly.
It was a property of matter, a capacity of space to restore itself after deformation.
How did you Transfigure a property?
A stone could become a cup, a cup could become a bird, but what about the stone's hardness?
Hardness changed as a consequence of Transfiguration, not as its target. He'd never cast a spell at hardness itself. The stone changed, and hardness followed.
Spatial elasticity worked the same way. He altered the structure of space, and the elasticity shifted accordingly.
But the restoring force, that stubborn pull back toward the original state, remained. It hadn't been truly changed, only compressed, suppressed. Withdraw the magic, and it sprang back.
Was that even a valid approach?
He looked up at McGonagall, voice uncertain, doubt clear. "Spatial elasticity... can be Transfigured?"
One corner of McGonagall's mouth lifted. The arc was small, but Regulus was certain he saw it.
McGonagall stood and raised her wand.
She pointed above the desk. Space deformed, identical to what Regulus had done, a fold suspended in the air above the surface.
Her wand stayed trained on it, and a second current of magic seeped from the tip.
"What you did," her voice carried the same measured cadence she used for classroom instruction, "was Transfigure the form of space. That's the first layer. The shape of space changed, but the elasticity remained. Elasticity is a separate property from form, and to stabilize the transformation, you need to address both at once."
She lowered her wand. The fold remained. No dissolution. No rebound. It hung there, still and quiet.
Regulus stared at the crease and spread his perception outward.
He felt space itself. He felt the shape of the deformation. He felt the restoring force, wrapped in a second layer of magic, pinned down.
Two layers of Transfiguration, stacked. One deep, the other deeper.
He could perceive the elasticity of that space existing as something tangible, something real.
His perception plunged another level. Spatial properties.
Before, he'd known space was elastic, that it tended toward restoration. But that had been physics, knowledge from a textbook. Not something he'd perceived.
Now he perceived it. No longer an abstract concept. Something concrete enough for magic to touch.
McGonagall gave him no time to dwell. She raised her wand again and fired a Lumos charm into the fold.
The orb of light drifted from her wand tip, entered the deformed space, and was torn apart.
Countless tiny points of light ricocheted through the grooves of the crease, a swarm of trapped fireflies, unable to find their way out.
McGonagall lowered her wand, sat back down, and picked up her teacup for another sip.
As the rim touched her lower lip, her eyes narrowed slightly, savoring something fine.
"Any more questions?" She studied the teacup, not looking at him.
"No." Regulus stood and bowed. "Thank you, Professor. That was enormously helpful."
A beat. He decided enormously might not be enough. "More than helpful. You've opened a door."
McGonagall glanced up. Her mouth curved, faintly, before she lowered her head and returned to her tea.
After a moment she looked up again. "Problem solved?"
Regulus's manner grew more deferential. "Not yet. But the path is clear. What you showed me, I perceived something deeper in space that I couldn't before. Now I know what to do."
McGonagall regarded him and nodded once. "Until your Spatial Transfiguration matures, don't fire spells into it."
"Understood."
"Thank you, Professor." He stood, bowed deeply, and turned toward the door.
Sirius sat in his chair, motionless, until Regulus pulled the door open. Then something jolted through him and he shot to his feet.
They left the office. The door closed behind them.
Late November sun had already dropped low. The corridor dimmed around them, torches flickering to life in their iron brackets along the walls, one every few paces.
Nearly dinnertime. The corridor was deserted; everyone had gone to eat.
Regulus walked ahead. Sirius trailed a few steps behind. Neither spoke.
Regulus's mind was still working.
He'd been wrestling with that restoring force the entire time.
He knew space snapped back after deformation. That was basic physics. Elastic modulus. The structural tendency of space to return to equilibrium.
He'd accepted the fact and fought against it, pressing with magic, bracing with willpower, holding the deformation in place, refusing to let it rebound.
The effort had been brutal. Under a minute, heavy magic drain, heavy mental drain.
But McGonagall's approach was nothing like his. She hadn't fought the elasticity at all. She'd Transfigured it, treated that restoring force as a concrete problem that Transfiguration could solve.
The realization landed hard: he relied too heavily on rational analysis to break problems apart.
He'd treated this as a physics problem. Reduced spatial elasticity to an abstract physical concept, analyzed it, calculated against it, opposed it.
Every step was logically sound. Every step had theoretical backing.
He'd been right. And exhausted.
In his framework, spatial elasticity was a physical property of space itself. An abstract attribute. The idea of making it a target for Transfiguration would never have surfaced naturally from his logic.
Physics was one language for describing how the world worked. Magic was another.
Using physics to think through magical problems sometimes worked. Sometimes it didn't.
This time it hadn't. But the physics wasn't wrong. The error was letting physical reasoning lock the problem into a box.
His magical path had been confirmed long ago: reason and intuition, walking together.
But confirming it was one thing. Hitting a specific problem was another.
When a problem appeared, his first response was still to analyze, decompose, find the pattern, find the cause, find the solution.
Rational thought took the lead, almost by reflex.
That reflex had its value. Rational thought had carried him far.
The Decomposition Curse had been built that way. Spatial magic had been calculated that way. The foundational logic of Light Source Magic had been derived that way.
Every one of those achievements rested on rational thinking. Without it, none of them would exist.
But on this particular problem, rational thinking had led him astray.
He'd forced a problem that needed an intuitive breakthrough into the shape of a technical puzzle.
McGonagall's single demonstration had shown him: this wasn't a technical problem. It was a problem of approach.
He'd hit a boundary. Rational analysis had described the problem perfectly but couldn't find the solution.
Because the solution lived on the other side, in intuition, in magic, in treating an abstraction as something that could be directly acted upon.
The two modes of thought weren't opposed. He'd always used both, only weighted them differently depending on the problem.
This time the weighting had been wrong. Too deep in the physics. Too little of magic's instinct.
Regulus had always solved problems by taking them apart. Break it open, see it clearly, solve each piece.
The method worked, and it would keep working. But he couldn't only disassemble.
Some problems, you take apart until you reach the last layer and find that you recognize every component, and the problem still isn't solved.
That's when you need a different angle. Stop pulling downward. Look sideways. See how someone else does it.
Like today. McGonagall demonstrated once, and I understood instantly.
But that's fine. Rational thinking is my strength. I won't abandon it.
I only need to add one thing on top of it: when I hit a boundary, knowing where to look.
He walked on, pace unhurried, thinking as he went.
Sirius trailed behind him, silent the whole way.
Regulus had nearly forgotten anyone was there when Sirius spoke, his tone forced into something deliberately casual.
"Regulus."
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