On the train to Hogwarts, Ron had shown Hermione and Neville that classic trick of changing Scabbers's color.
It was hard to say whether he had succeeded.
He had indeed turned Scabbers's brown fur a slightly brighter deep orange, but it was nowhere near the yellow he had intended.
Even that had surprised Hermione a little at the time, mostly because she wondered how such a bizarre spell could exist.
Compared with Ron's crude Transfiguration, however, Professor McGonagall's Transfiguration Spell was far more accomplished. The rat Tris had placed on the desk immediately became an exquisite Crystal Goblet engraved with intricate patterns.
"As I just explained," Professor McGonagall said, sweeping her gaze across the class. Once she was certain everyone was watching her, she turned back to Tris. "The difficulty in transfiguring living things lies in suppressing their living activity. Otherwise, a cup that moves would clearly defeat the purpose of turning it into that form."
As she spoke, she tapped the glass lightly with her wand.
The glass gave a clear chime without moving an inch.
"When that activity is suppressed, the will of the living creature is suppressed along with it. In other words, a successfully transfigured living creature is deprived of consciousness for the duration of the transformation. This brings us to another issue: animal will. Generally speaking, the more advanced the creature, the stronger its self-awareness and will.
"Besides the differences in volume and mass that must also be considered when transfiguring inanimate objects, the difficulty of transfiguring living things depends on the strength of their will and consciousness.
"The more advanced a creature and the stronger its consciousness, the harder it is to transfigure. Forcing a transformation on an intelligent being is beyond the capabilities of the vast majority of wizards.
"This greatly reduces the success rate of such Transfiguration, and even when it succeeds, its duration is significantly shortened."
"Professor!" Hermione raised her hand.
"Miss Granger." Professor McGonagall nodded.
Hermione stood and asked, "Then how do magical creatures and ordinary people compare in terms of how difficult they are to transfigure?"
"That is a good question." Professor McGonagall nodded approvingly. "It brings us to another variable affecting the Transfiguration of living things: magical interference.
"Although most magical animals are more intelligent than ordinary animals, there is still a considerable gap between them and wizards, Muggles, or other humanoid beings.
"That means there are also differences in their consciousness and will. Yet fantastic beasts are harder to transfigure than Muggles. This is because of their magic.
"The magic within fantastic beasts interferes with the changes a Transfiguration Spell makes to their bodies, making it difficult to achieve the effect we want. The more powerful the fantastic beast, the harder it is to transfigure.
"No wizard in recorded history has ever completely transfigured a phoenix or a dragon, for instance."
"Professor, does a wizard's magic interfere as well?" Hermione asked.
"Yes." Professor McGonagall nodded firmly. "However, wizards use magic differently from magical creatures. In terms of their own inherent magic alone, wizards usually fall far short of magical creatures they can easily defeat.
"In practice, therefore, although transfiguring a wizard is slightly harder than transfiguring a Muggle, it is usually less difficult than transfiguring a magical creature. That is, of course, assuming the wizard is unprepared.
"If magical protections are involved, that is naturally another matter. Does that answer satisfy you, Miss Granger?"
"Yes, thank you, Professor McGonagall." Hermione nodded.
"Answering an eager student's questions is something every teacher is happy to do. There is no need to thank me for it. Please sit down, Miss Granger."
Hermione sat down happily.
Professor McGonagall turned back to Tris. "Does that resolve your doubts, young Mr. Weasley?"
"Yes, Professor." Tris nodded obediently. Before Professor McGonagall could tell him to sit, however, he spoke again. "Professor, I'm sorry, but I just thought of another question..."
Professor McGonagall glanced at the clock on the classroom wall and nodded. "Very well, young Mr. Weasley. We still have enough time, but I hope this will be the last question of the lesson.
"After all, taking in too much information at once does not help you absorb knowledge and put it to use."
"Yes, Professor." Tris remained perfectly obedient. After Professor McGonagall indicated that he could ask, he pointed at the goblet on the desk that Scabbers had become.
"Is it possible for an object to be transfigured several times by several wizards, leaving several other transfigured forms beneath its current one? Would multiple Transfiguration spells conflict with one another?
"If an animal that was originally alive, such as Scabbers, has been turned into a goblet by you, Professor, would someone wanting to transfigure it again use Transfiguration for inanimate objects or for living things?
"And if another layer of Transfiguration were added, would a Reversal Spell restore it directly to its original form, or to its previous form?"
"A very imaginative question." Professor McGonagall nodded. "Let us do this, young Mr. Weasley: try transfiguring this goblet yourself."
Surprise and hesitation appeared on Tris's face, but a gleam flashed deep in his eyes.
So far, so good!
"Professor, something this large..." Tris looked at the goblet, appearing deeply uncertain.
"It is all right. Simply try turning it into something similar in size, mass, and material. That will greatly reduce the amount of magic required."
Tris nodded, took a deep breath, and cast a Transfiguration Spell on the crystal glass.
The crystal glass twisted and became a slender Crystal Vase. Although its shape had changed considerably, its material, volume, and mass differed very little.
"You clearly have your answer regarding which kind of Transfiguration to use," Professor McGonagall said with a smile. "An animal that has already been turned into an object can be transfigured using Transfiguration for inanimate objects.
"And I imagine you also have your answer regarding overlapping magic. A new Transfiguration does indeed affect the existing one, greatly shortening its duration. Likewise, although casting a new Transfiguration on something with an underlying transformation is no more difficult, its duration will be greatly reduced.
"If the underlying Transfiguration ends first, however, the result depends on the circumstances. Take this vase, for example. Its underlying form is a rat. Its intermediate form is a drinking glass, which was then turned into a vase.
"But if my Transfiguration of the living creature dissipates first, the inanimate-object Transfiguration cast by young Mr. Weasley will lose the foundation that makes it possible and collapse outright.
"Now, class, let us think a little further. If there are three or more layers of Transfiguration at once, and one of the intermediate layers is removed first, what would happen?"
Seeing the young wizards all sink into thought, Professor McGonagall made no attempt to answer. She merely said, "I shall leave that as a question for you to consider over time. Or, once your magical skills have improved, you may try it yourselves."
At that point, she looked at Tris.
"As for young Mr. Weasley's final question, I can answer it directly. An ordinary Reversal Spell usually reverses only one layer of Transfiguration.
"Unless the wizard casting it has exceptionally powerful magic and deliberately expends a large amount of additional power. Wizards do not usually do that, however. And if a wizard suspects multiple Transfiguration Spells are involved, there is actually a simpler way to handle it."
As Professor McGonagall spoke, she raised her wand toward the Crystal Vase and recited an incantation longer than any basic spell Tris had encountered, then gave the vase a light tap with her wand.
The vase immediately began to twist and stretch.
"The Forced Reversal Spell, an advanced form of the Reversal Charm, can directly restore a transfigured object to its state before it was altered by magic... hmm?"
Professor McGonagall's voice cut off abruptly.
The vase before her had first turned into a crystal glass, then into a rat.
Everything up to that point had been just as Professor McGonagall expected. She had been about to say, "Just as this Crystal Vase will ultimately return to being a rat."
But the rat was still changing.
The large brown rat began swelling like an inflating balloon.
"Scabbers?" Ron watched the rapidly growing rat, disbelief and panic mingling on his face. He had no idea what was happening.
Nor was he alone. Apart from Tris, none of the students present knew what was happening. They had clearly seen Professor McGonagall turn the rat into a crystal glass, and then the glass become a vase.
Reversing the transformation should have returned it to a rat. Why was the rat changing again?
Had Professor McGonagall cast another Transfiguration Spell on it?
The students did not understand what was unfolding before them, but Professor McGonagall had already realized the truth.
An Animagus!
The rat before her was actually an Animagus!
Although a completed Animagus transformation was indeed extremely difficult to identify from the outside, Professor McGonagall was the most renowned Transfiguration expert in the wizarding world. Having an Animagus right under her nose for so long stirred an irrepressible surge of anger in the normally unflappable professor.
Whatever the reason, an Animagus disguising themselves as an animal and hiding beside a young wizard was not normal.
Capture them first!
Professor McGonagall made that decision almost instantly.
The rat's body was still growing when Professor McGonagall flicked her wand. In the blink of an eye, the long desk in front of Tris, Harry, and Ron transformed into an enormous Metal Mesh Cage.
The growing rat-or rather, the person returning to human form-was trapped inside.
It worked!
Tris watched the changes unfold, his expression one of surprise and confusion. Only in the deepest recesses of his eyes was there a trace of relief.
He had spent a long time secretly planning and scheming for this moment. He had learned about Transfiguration through various means, all to devise a way for Professor McGonagall to capture this rat-or rather, Peter Pettigrew.
There had been more than one possible method, and he had prepared contingencies for many of the variables involved.
Things had gone even more smoothly than he had expected!
Professor McGonagall was especially tolerant of students who loved learning, so the fallback plans he had prepared in case she became wary had proved unnecessary. Tris could happily remain unnoticed.