Bones observed Crouch's reaction and keenly sensed that something was amiss. Given the circumstances, Dumbledore had simply been a bit impolite, but Crouch's reaction was far too strange.
There was something in that room that was not meant to be revealed. Bones quickly identified the source of the abnormality.
What could it be? She wondered in her mind.
By then, Dumbledore had already entered the room where the noise had come from. He had already learned from Tom about Crouch's little secret. Tom's excuse had, in a way, been quite convincing: while conversing with the Dementors, he had learned of something slightly unusual—an individual had died in Azkaban. This, in itself, wasn't strange, as many people died in Azkaban when they couldn't endure it any longer, but the Dementors claimed it wasn't the same person who had been locked up.
Though Tom found this odd, the Dementors cared little for such matters as it was a conflict among wizards and had nothing to do with them. As long as the number of prisoners was correct, it sufficed for them.
The Dementors were rather carefree; they patrolled daily, absorbing the emotions of the prisoners while simultaneously guarding them to prevent escapes. After Sirius Black's escape, the Dementors conducted searches so actively mainly because during their external missions, they could absorb the emotions of certain individuals they encountered, with the Ministry of Magic's approval. As for Sirius Black, if he escaped, he simply escaped; it wasn't a big deal.
That's why they were angry after being expelled from Hogwarts and removed from Hogsmeade: no food, naturally, made them irate.
The explanation Tom had provided was much more convincing than claiming he deduced everything through star observation/evidence in the crystal ball/dreams. So, Dumbledore genuinely believed him. He had come to Crouch's house today to verify Tom's claim. All the actions he had taken so far were to distract Crouch and lower his guard.
After hearing the noise, Dumbledore made a resolute decision. Today, he had to search Crouch's entire house. He pushed open the door of that room, and even though it was empty, Dumbledore immediately directed his gaze to a corner of the room.
The empty room bolstered Crouch's courage a bit. He straightened up, and just as he was about to say something, he saw Dumbledore draw his wand.
"Homenum Revelio."
In fact, Dumbledore was doing something entirely unnecessary. He could cast the "Homenum Revelio" spell without words and without a wand. In the face of this spell, the invisibility cloak, the real invisibility cloak, was as useless as if it didn't exist, including the Deathly Hallows Invisibility Cloak, which couldn't escape Dumbledore's scrutiny.
Dumbledore was arguably the best wizard in the magical world when it came to using the Revelio Charm because he knew it so well that it was almost a reflex, turning an active skill into a passive one, much like his Legilimency, which he could use without a wand or voice.
(There are reasons to believe that Dumbledore used the "Homenum Revelio" spell every time he entered a new environment, as when he and Hagrid first entered Hagrid's hut, they immediately spotted Harry and Ron under the Invisibility Cloak... that's the best evidence.)
Although Dumbledore used this spell as if it were a passive skill, in the magical world, people who can use this spell are extremely rare. So far, only two people have been able to consistently and silently perceive the Invisibility Cloak: Dumbledore and Moody, who achieved it through his magical eye.
But Dumbledore still drew his wand and recited the spell.
As if a gentle breeze passed by, a young man with messy light blond hair appeared before the eyes of the three.
Bartemius Crouch's face turned ashen instantly.
Bones, after clearly seeing the young man's face, also changed her expression: she knew this person, he was named Barty Crouch Jr., Crouch's only son.
This man, as it was supposed, had been personally sent to Azkaban by his father over ten years ago and died in prison. How could he possibly appear here?
Bones glanced at Crouch's cadaverous face and had a daring thought: had Crouch done something improper?
The young man had an expressionless face, his skin pale from being confined at home for so long, making the freckles on his face even more prominent. His demeanor was strange, as even when Dumbledore and the others suddenly appeared in front of him, the young man showed no reaction.
Dumbledore approached the young man, observed him for a few seconds, and then turned to Crouch with a tone of regret. "Barty, I really didn't expect... How long did you use the Imperius Curse on your son?"
"Imperius Curse!" exclaimed Bones, looking incredulously at Crouch. In her impression, Barty Crouch Sr. was an upright and ruthless person, but now that image was crumbling in a matter of minutes: abuse of power, switching places with his son, and using the Imperius Curse to control him for so long...
Barty Crouch Sr., how many more things does the Minister of Magic not know about you?
Barty Crouch Sr. had completely given up resistance. He was like a criminal whose criminal methods had been exposed by a detective and began confessing all his deeds of the past ten years.
It turns out that after young Crouch was imprisoned, his mother fell into deep sadness and finally, before her death, begged her husband to rescue their son from prison. Crouch agreed because he truly loved his wife. So, during a visit to the prison, young Crouch ingested a Polyjuice Potion containing his mother's hair, while Mrs. Crouch took another potion containing her son's hair.
In this way, they switched identities and appearances.
Thus, Barty Crouch Sr. managed to deceive everyone and get his son out of Azkaban. Mrs. Crouch, on the other hand, was left behind in Azkaban in endless despair. Despite it all, she didn't forget to regularly take the Polyjuice Potion, even up until her death.
Therefore, when she died, she still looked like Barty Crouch Jr., and everyone, including Bones, thought it was Barty Crouch Jr. who had died in Azkaban.
After getting Barty Crouch Jr. out, Barty Crouch Sr. publicly announced his wife's death and held a secret funeral. In reality, if someone were to dig up Mrs. Crouch's grave, they would find the inside empty.
Since then, Barty Crouch Jr. had been confined in the Crouch Mansion, living under the Invisibility Cloak and cared for by the house-elf, Winky, until Dumbledore and the Minister of Magic unexpectedly arrived.