The Book of Mysteria is a mysterious, ancient tome of unknown origins. The spells and potions contained within its pages are occasionally dark but were certainly too dangerous for the book to be allowed to fall into the wrong hands.
History of the Book
The Book was held at Beauxbatons just prior to traveling to Hogwarts for keeping. In transit, the Book was accompanied by the Headmaster and several Beauxbatons staff members to help keep it safe. During their travels, the group was attacked and killed by Voldemortist's followers, and they impersonated the school staff for almost an entire year (Term 6) at Hogwarts.
The Book at Hogwarts
Prior to coming to Hogwarts, the Book of Mysteria traveled from location to location secretly, never being held in one place for any length of time. It was well known that Voldemortist had an interest in finding the Book and plumbing it for secrets to overcome death and gain power. Although the passing of the book to Hogwarts was supposed to be a secret, Voldemortist knew it was there and Headmaster Kobus Hendrik took precautions to protect the Book and the school.
During Term 6, Slytherin ghost Marcella Riddle chanced to discover the Draught of Ephemera in the Book. She immediately shared her discovery with the school staff and other recent House ghosts. The staff divided on the issue: some felt that any effort to return those whose life had been taken prematurely was a worthy one while others felt that going against the natural course of things was a mistake. Still, Headmaster Kobus decided to go ahead with the brewing, and ghosts Riddle, Anjelica Lainey, and Kris Airlia decided to attempt the dangerous journey to regain their bodies.
Brewing took most of the term, and by the time the potion was ready, Voldemortist had penetrated the castle grounds and lurked outside the school. He timed his attack well, so that he struck just as the potion came ready and the majority of the staff were occupied. Several students were killed at the Groundskeeper's cottage, and the students were confined to the castle.
With Professor Phoebe Phoenix acting as medium, ghosts Riddle, Lainey, and Airlia were all successfully returned to their former bodies. Airlia had been dead for 70 years, and her new physical form was that of a very old woman. Due to her extreme fraility and the relative weakness of the others involved in the process, the group moved to the Hospital Wing.
At this time, Voldemortist stormed the castle, continuing his massacre as he proceeded. Kobus and many staff members were occupied in the Hospital Wing, leaving Professor Cassandra Rae to battle Voldemortist through the castle to the Spirit Room. She was stabbed during the attack, and Voldemortist managed to escape with the Book in hand. Abandoned and dying, Rae was near death with no one in the school realizing she was injured or knowing she needed help.
In a heroic gesture, the Gryffindor ghost Sir Spots attempted to complete the ritual using the remaining Draught and using Rae as his medium. If he could regain his physical form, he would be able to assist Rae and keep her from dying. Sadly, Rae was too weak to be a proper catalyst for the ritual, and Sir Spots passed on before he could be returned to his physical body. It is impossible to know if his brave sacrifice allowed the noble Sir Spots to finally be laid to rest, or if his disappearance was a result of the Draught.
In a miraculous move, Professor Lainey knew that the issue with Voldemortist had not been resolved, and she dragged herself from her bed. With the help of the Slytherin and Hufflepuff prefects, Lainey staunched Rae's bleeding and took her back to the Hospital Wing for recovery.
In the meantime, Professor Hendrik left the Hospital Wing to do battle with Voldemortist, who was heading for the Forbidden Forest in hopes of reaching an apparition point, with the Book of Mysteria in hand. After a spectacular duel, Voldemortist made it to the apparition point. However, just as he disapparated, Professor Hendrik managed to summon the Book of Mysteria from Voldemortist's weakened grasp.