Settled in the story
Where did the Half-Blood Prince's spells first appear?
Levicorpus hangs a boy upside down in book five with no author attached. A year later an annotated textbook hands the same spell to Harry, and the trail ends with Snape naming himself — and a memory that explains the name, the spells, and the grudge in a single sitting.
This thread gives away a resolved story point
The clue
Two of the Prince's inventions turn up before his book does — one of them used against their own inventor, in front of a crowd, by his worst enemy.
The trail
- Book 5 · Snape's Worst Memory
In the Pensieve, a teenage James Potter hangs Severus Snape upside down by the ankle for a laughing crowd. The spell is Levicorpus: nameless, authorless, fashionable that year. Nobody in the memory asks who invented it. That silence is the plant.
- Book 6 · The Half-Blood Prince
Harry inherits a battered copy of Advanced Potion-Making covered in somebody else's margin notes. Among the scribbles is Levicorpus, claimed by the book's previous owner, the self-named Half-Blood Prince. The school craze from the memory turns out to be one student's invention, leaked out of his own textbook.
- Book 6 · Sectumsempra
Another margin note, marked for use against enemies, cuts Draco Malfoy open in a flooded bathroom. Snape arrives and heals the wounds with a counter-curse he has no innocent reason to know by heart — then demands to see Harry's textbook. The healer has recognised the handwriting of the weapon.
- Book 6 · Flight of the Prince
On the grounds after the tower, Snape says it plainly: the spells are his, invented by him, and he is the Half-Blood Prince. Harry has spent a year fighting his teacher with the teacher's own schoolwork.
- Book 7 · The Prince's Tale
The last memories close the loop: a lonely student filling margins with spells of his own, a mother named Eileen Prince behind the chosen name, and a boy proud enough of his private genius to sign his work — who then lived to be tormented by it in front of everyone.
The payoff
The Prince is Severus Snape, named for his mother's family. His spells escaped into the school a generation before Harry found the book, which means the cruellest scene in book five was staged with the victim's own invention. The plant was loaded before the book that explains it was ever opened.