Seeing the last sentence in the notes, Sherlock was silent for a moment.
These were clearly notes left by the Original Owner's mother, Sally Forrest, and the date they were written must have been just before her incident.
Her thinking must have still been normal at this time; after completing what was mentioned in the notes, she turned into a madwoman.
Sherlock silently picked up the notebook on the desk and began reading from the first page.
"Looking at Sherlock now, I feel he is the continuation of Victor's and my soul. Having a child is something enough to make every woman crazy with happiness. I have always considered myself the most rational of all Wizards, but even now, I still feel as though I am filled with happiness."
"In the days of taking care of the newborn Sherlock, I thought back to when I was tortured by the Cruciatus Curse, which caused cracks to appear in my soul."
"To create that soul mending magic, I researched a great deal of material on soul magic. Although I didn't achieve final success due to a lack of material for the 'thread,' I feel I have reached the forefront of the Wizarding World regarding knowledge of the soul."
"But the more I know, the more I feel my insignificance in the face of that endless knowledge. The soul is an incredibly complex subject. Very few spells have undergone in-depth research regarding the soul, yet every spell is closely related to the soul."
"Sherlock's birth made me want to take up this research again. The soul is undoubtedly a powerful force. I feel I can use this power to give Sherlock a gift. Even if I were to have an accident and not be around in the future, this thing could still replace me and always be by his side."
The first few pages were like Sally's personal journal. Later, she built this underground study beneath her own home, placed all the books related to the soul that she had collected over the years into it, and began her research into soul magic.
Whenever there is magical experimentation, there must be experimental subjects, and the subject Sally chose was none other than herself.
Sherlock's mother was clearly a ruthless person. Her own soul was already fractured, yet she still recklessly performed various unstable magical experiments on it.
She wanted to use the power of the soul to create a spell—a spell that could protect another soul from harm.
Because all spells in the Wizarding World are related to emotions.
To use the Full Body-Bind Curse, one must first have a strong desire to immobilise the opponent.
To use Apparition, one must firmly believe that one can reach the destination.
To use the Killing Curse, one must possess extreme darkness and the most resolute killing intent in one's heart.
These are all emotions that Wizards must genuinely feel from the bottom of their hearts and express.
This is also the reason why Wizards rarely possess rationality and logical thinking.
They spend most of their time casting spells under intense emotional states. Sentimentality has become their habit; remaining in a rational state for prolonged periods would instead weaken their magical ability.
And since the physical body serves as the foundation for life, where do all of a person's emotions and desires come from?
The answer can only be the soul.
If a person lacks all desires and emotions, then even if their body is alive, they are essentially no different from someone who is dead.
For example, the Dementor's Kiss essentially sucks away all of a Wizard's positive emotions, turning the victim into an empty shell. Even if the heart is still beating and blood is still flowing, that person is effectively dead.
That is why it is said that, although there are few spells in the Wizarding World directly related to the soul, almost all magic is related to it.
Since magic is formed through the soul and ultimately exerts its influence on external reality, the soul must also possess the ability to block these influences and negate their effects.
Other spells are straightforward enough, but the most critical one is the Killing Curse, which directly targets the soul.
The reason there are only three Unforgivable Curses is that, in the entire Wizarding World, only these three wicked spells have no counter-curse.
The other two, the Cruciatus Curse and the Imperius Curse, are not inherently fatal, but the Killing Curse can truly be called the nightmare of all living beings.
The effect of this spell manifests directly upon a person's soul. The creature struck dies at the level of the soul, while the body remains outwardly unharmed.
And apart from physical barriers, there is no spell that can block or break it.
If Sally's idea could work, then the Soul Protection Charm she envisioned could even block the Killing Curse.
For this, she conducted countless experiments.
In the experiments involving the Killing Curse, she naturally did not continue using her own soul as the test subject. Instead, she brought in many rabbits and mice, using these creatures with weaker souls as the earliest experimental subjects.
Sally's talent for magic was exceptionally brilliant. After a long period of research, she actually discovered a method for the Soul Protection Charm.
"...Rabbit No. A132 eventually survived. This is a surprising discovery, proving that the direction of my research is correct and feasible."
"However, Rabbit B341, which provided soul protection for No. A132, died. Essentially, this does not truly use the power of the soul to negate the Killing Curse; it can only be considered one life exchanged for another."
"The Killing Curse showed signs of rebounding when it struck No. A132 while under soul protection. This is somewhat similar to the Shield Charm; it may be because my line of thinking when designing this spell was somewhat influenced by the Shield Charm."
"And the surviving No. A132 also displayed some magical rejection reactions."
"Hmm, these are all important experimental data. After collecting them, I can keep a copy in the Hogwarts library, just like the soul mending magic last time."
Afterwards, Sally continued refining the Soul Protection Charm and eventually entered the stage of human experimentation.
Once again, she did not look for anyone else, but continued using her own soul as the experimental subject.
The effect that soul magic could ultimately negate or rebound the Killing Curse had already been confirmed through animal experiments, so the subsequent experiments no longer carried such fatal risks.
Sally discovered that if a human wished to cast this powerful Soul Protection Charm, the caster needed to possess an extraordinarily intense emotion towards the person being protected.
And that emotion had to be positive; simply put, it had to be love.
Whether it was a father's love, a mother's love, or romantic love, one had to possess profound love for the person they wished to protect.
Without such an emotion, the spell would not work.
And once the spell was successfully cast, the souls of the protector and the protected would become connected. Even if the protector died, the Soul Protection Charm would continue to protect the other person.
After all, this was protection at the level of the soul, and this was a world where ghosts and the dead truly existed.
Even death caused by the Killing Curse would not completely erase the victim's soul, but instead leave it bound to the killer.
Therefore, once the Soul Protection Charm had been successfully cast, the spell would not be broken even if the protector died.
Finally, after completing this spell, Sally linked her soul with Sherlock's, forming a Soul Protection covenant.
This was also the final gift she gave to the Original Owner.
After completing this spell, she left Sherlock's side, and when she appeared again, she had already become the madwoman she would remain thereafter.
Sherlock finished reading the experimental notebook, his emotions incredibly complicated.
The Original Owner's mother was undoubtedly a remarkable person. She claimed she was not a qualified mother, yet she had already done everything within her power to protect the Original Owner.
But in the end, the Original Owner still died—not because of anyone's magic, but after falling from an upstairs window during a reckless magical experiment, striking his head on the ground.
Such a simple physical injury, with no damage to the soul, naturally could not be prevented by the Soul Protection Charm.
After Sherlock arrived and took over this body, the protection magic assumed that the Original Owner's soul had merely been damaged, causing it to split.
That, in turn, led him to discover the "Soul Mending" spell hidden within the Restricted Section of the Hogwarts library.
Later, Sherlock's transmigrated soul and the Original Owner's unconscious soul were stitched together using the thread formed by Riddle. Now, the Original Owner and Sherlock were truly inseparable.
Sally's Soul Protection Charm was protecting both the Original Owner and, by extension, Sherlock.
Sherlock stood there in silence for a long time, staring at the experimental journal before finally letting out a sigh.
Just then, he suddenly remembered something.
In the first Harry Potter film, Philosopher's Stone, which he had watched in full in his previous life, the magic Harry's mother, Lily, had used to protect Harry from Lord Voldemort's Killing Curse was extraordinarily similar to the Soul Protection Charm Sally had developed.
Sherlock also remembered that, when Harry asked Dumbledore about the scar on his forehead at the end, Dumbledore had told him it was his mother's love.
Wasn't that exactly the prerequisite for the Soul Protection Charm?
It required the protector to possess deep love for the person being protected.
Sherlock stood there, stunned.
Since this spell had been invented and developed by Sally, how had Lily learned it?
The experimental journal never mentioned the name Lily Evans.
When the spell was created, Lily would only just have begun attending Hogwarts and could not possibly have come into contact with such advanced magical research.
After realising this, Sherlock flipped through the journal from beginning to end once more before stopping at a passage he had noticed earlier but not paid much attention to.
"Hmm, these are all important experimental data. After collecting them, I can keep a copy in the Hogwarts library, just like the soul mending magic last time."
When the experiment reached this stage, Sally had gone to the Hogwarts library and deposited a copy of her research there.
A look of sudden understanding appeared on Sherlock's face.
Then it was highly likely that Lily had discovered this spell in the Hogwarts library, learned it, and later, after Harry was born, linked her own soul to his.
Afterwards, Lily fell after being struck by the Killing Curse, but Harry relied upon the power of the protection spell to rebound Lord Voldemort's curse, surviving and becoming the Boy Who Lived.
Everything connected.
No wonder Dumbledore had told him that the crescent moon mark represented his mother's love.
The Soul Protection Charm truly was a spell that could only be cast through love. Once the protection was established, it could even rebound the Killing Curse.
Sherlock silently placed the experimental journal back where it had originally rested on the desk. He took nothing from the underground library.
Everything in this study had been built upon a mother's love.
She may have become a madwoman afterwards, driven by other people and other circumstances. She may have cursed and scorned her son, and failed to fulfil a mother's responsibilities in later years.
But she was still a great mother.
While Sherlock stood lost in thought over the experimental journal, Amy seemed to notice the heaviness in his mood. She said nothing, merely blinked quietly and waited beside him.
The sky gradually darkened. By this time, little Sherlock had already returned home from school, and the nanny hired by his father, Victor, had also arrived to prepare dinner.
None of them realised there were two uninvited guests beneath the courtyard.
Before leaving the underground study, Sherlock carefully relocked every door, leaving no trace that anyone had been there.
The entrance to the study was also extremely well hidden among the overgrown weeds in the garden. Unless someone walked directly to it, they would never discover it.
After reading all the experimental journals, Sherlock took Amy's hand and left the underground study.
He glanced once at the warm yellow lights glowing inside the house. He had no intention of seeing the younger Sherlock and simply took Amy's hand, Apparating directly back to London.
Their figures instantly appeared in a quiet alley.
Sherlock stood there for a moment, steadying his emotions before taking Amy out to fulfil the promise he had made earlier—to treat her to a proper meal.
They went to a Muggle restaurant Kingsley had once taken Sherlock to. Originally, Sherlock had only intended to give it a try, never expecting it to have already been open fourteen years earlier.
Amy had a very small appetite, but simply being able to eat out, while admiring the night-time view of London, was a completely new experience for her.
After dinner, they did not return immediately. Sherlock bought Amy a colourful pinwheel, and together they walked across London Bridge.
Amy leaned against the railing, holding the pinwheel in one hand. The breeze spun the pinwheel and gently lifted the blonde hair from her forehead.
Sherlock looked down at the River Thames beneath the bridge, his heart filled with emotion. On the surface, this journey seemed to have gained him nothing, yet in reality, he had gained a great deal.
He turned to look at Amy.
The flashing neon lights reflected across her face. It was obvious she was happy, yet the corners of her lips remained still, as though she had forgotten how to smile.
Sherlock reached out and gently pinched her cheeks, helping her form a smile as he whispered,
"This world is beautiful, Amy. There are people we love, and people who love us, so remember to smile more."