No one truly knows all of Hogwarts secrets; not even the great Albus Dumbledore would claim such. Throughout history, many witches and wizards have sought to discover the truth hidden with her walls. But Hogwarts protects her secrets, keeping her magics buried deep within.
One of the greatest mysteries is the magic that created the Book of Admittance, which records the birth of every magical child with British. Many attempts have been made to replicate this spell, but the closest that any have come is the Underage Sorcery Detection Net that is used to detect underage magic.
The reason that every attempt has failed is not due to it being based upon accident magics lost to time, nor does it require an unbelievable amount of magical power to cast. No, the reason these attempts have failed is that they are operating upon the assumption that it was either Rowena Ravenclaw or Salazar Slytherin who created the spell, when it was in fact Helga Hufflepuff. Often dismissed as the least of all the founders, Helga was in fact a master of one of the most dangerous magics: ley magic.
When each witch or wizard is born, their magic separates from their mothers, creating a unique magic signature. This energy signature resonates with the ley lines. Helga created a spell that detected these resonances and scribed the information within the Book of Admittance. Once this signature was registered within the book, all future students' whereabouts were tracked so that they could be sent their letters. Even if they were outside of the British ley lines’ reach, the spell could track them
Unbeknown to Helga Hufflepuff, it was not just the magic within a witch or wizard that caused ley lines to resonate. Other energies could cause a near identical resonance. And that is what happened one day when a blue police box appeared within Leadworth. A man with brown, floppy hair and wearing a bowtie exited the box. He turned to smile at the woman who followed him out. He lent forward for a kiss and brushed a blond curl of hair back behind her ear. The woman smiled at him and then looked down at the child she carried in her arms. Though only a few months old, it was clear that the child has inherited her mother's wild curls and her father's hair colour.
The exact moment that the blond woman carrying the child stepped upon the Earth, the Book of Admittance’s quill sprang to life. And it wrote the following name: Hermione Amelia Song