Harry Potter and the Half-Blood Prince (Severus Snape)

Harry Potter's relationship with the Half-Blood Prince's potions textbook is a central, transformative, and ultimately tragic arc in his sixth year at Hogwarts. The book, an old copy of Advanced Potion-Making filled with handwritten corrections and invented spells, elevates Harry from a mediocre potion-maker to Slughorn's star pupil, but its true owner—Severus Snape—and the dark nature of its most powerful spell, Sectumsempra, lead to a catastrophic confrontation that shatters Harry's trust and contributes directly to Dumbledore's death.

Discovery and Early Reliance

Harry first encounters the book during his initial N.E.W.T.-level Potions lesson with Horace Slughorn. Having not expected to continue the subject, Harry borrows a battered copy of Advanced Potion-Making by Libatius Borage from Slughorn's store cupboard. He is immediately annoyed to find the margins covered in scribbles, but when he follows an alternative instruction to "Crush with flat side of silver dagger, releases juice better than cutting," his potion, the Draught of Living Death, turns exactly the shade of lilac described by the textbook, while Hermione's remains stubbornly purple. This success wins him a bottle of Felix Felicis, Slughorn's prize for the best potion. The book's owner identifies himself only at the bottom of the back cover: "This book is the property of the Half Blood Prince." Harry quickly comes to rely on the Prince's instructions, which consistently yield superior results, earning him Slughorn's effusive praise and a reputation for talent he does not genuinely possess. The Prince's notes are not limited to potions; they include directions for what look like self-invented spells, including Levicorpus, a nonverbal jinx that hoists a person by the ankle, which Harry successfully tests on a sleeping Ron.

The Prince's Spells and Hermione's Suspicion

Harry's growing dependence on the Prince's book creates a rift with Hermione, who is deeply suspicious of its origins and contents. She argues that the Prince's spells, like the toenail-growing hex and Muffliato, which fills nearby ears with an unidentifiable buzzing, are irresponsible and potentially dangerous. Harry dismisses her concerns, pointing out that the Prince's bezoar tip saved Ron's life when he was poisoned by a goblet of mead meant for Dumbledore. The book becomes a kind of guide and friend to Harry, a source of secret knowledge that makes him feel powerful and clever. He even goes so far as to disguise the Prince's copy by swapping its cover with a new book from Flourish and Blotts, so he can keep it without raising suspicion. Hermione, in contrast, remains resolutely committed to the "official" instructions, growing increasingly bad-tempered as they yield poorer results than the Prince's. Her research eventually uncovers that the "Half-Blood Prince" is Eileen Prince, the mother of Severus Snape, a revelation Harry dismisses, insisting he can tell the Prince is a man from the way he writes.

The Sectumsempra Catastrophe

The climax of Harry's reliance on the Prince comes in a confrontation with Draco Malfoy. After finding Malfoy crying in a bathroom, Harry instinctively uses a spell he had marked in the book, captioned "For enemies": Sectumsempra. The spell causes deep, bloody gashes to appear on Malfoy's face and chest, nearly killing him. Snape arrives and heals the wounds, then demands to see Harry's schoolbooks. Harry, in a panic, hides the Prince's book in the Room of Requirement, replacing it with Ron's copy. When Snape examines the book, he finds the name "Roonil Wazlib" written inside the cover—a nickname Ron's spell-check quill had produced. Harry claims it is his nickname, but Snape is not fooled. He gives Harry detention every Saturday until the end of term, a punishment that prevents him from playing in the crucial Quidditch final. The incident shatters Harry's faith in the Prince, forcing him to confront the dark nature of the magic he had been so casually using.

Revelation and Rejection

The true identity and significance of the Half-Blood Prince are revealed during the flight from Hogwarts after Dumbledore's murder. When Harry chases Snape across the grounds and attempts to use the Prince's spells against him, Snape deflects them with contemptuous ease. He then reveals himself: "You dare use my own spells against me, Potter? It was I who invented them — I, the Half-Blood Prince!" The revelation is devastating. The clever, helpful guide Harry had admired is the same man he now hates more than anyone. The book, once a source of comfort and success, becomes a symbol of Snape's duplicity and Harry's own naivety. In the aftermath, Harry is consumed by guilt and anger, realizing that he had been learning Dark magic from the man who had betrayed Dumbledore and was responsible for his parents' death. The relationship ends not with a lesson learned, but with a bitter, personal betrayal that leaves Harry more isolated and determined than ever to face Voldemort alone.