The Story of Sectumsempra Spell: In Harry Potter and the Half-Blood Prince, Professor Minerva McGonagall, known for her sharp wit, assigns Harry Potter and Ron Weasley to Potions class under the guidance of the new professor, Horace Slughorn. Unlike the previous Potions Master, Severus Snape, who was known for his severe and intimidating nature, Slughorn is much more cheerful and welcoming. He greets the boys warmly and assures Ron, who is convinced he’s terrible at Potions, that he’ll help him improve.
After asking the boys to fetch their Potions textbooks from the cupboard, Slughorn starts the lesson. By sheer luck, Harry picks up an old but well-marked copy of Advanced Potion-Making, which turns out to be a game-changer for him.
Harry’s Advanced Potion-Making textbook, marked with the name “Half-Blood Prince,” becomes his secret weapon in Professor Slughorn’s Potions class. One of the standout moments happens when the book’s note suggests a special method for preparing the Draught of Living Death. Instead of just slicing a Sopophorous bean as the recipe states, the Prince’s annotation advises Harry to “crush with blade” to extract its juice more effectively.
Following this guidance, Harry brews the potion flawlessly, impressing Slughorn, who comments that it’s exactly as it should be. In recognition of his success, Harry is rewarded with a vial of Felix Felicis. However, his growing obsession with the book leads him down a darker path. As he becomes more reliant on its mysterious annotations, especially one involving a dangerous curse, Harry finds himself in trouble as the story unfolds.
Harry Casts Sectumsempra on Draco Malfoy
Harry becomes increasingly absorbed by the Half-Blood Prince’s book, unable to shake his curiosity. One day, he discovers a spell called “Sectumsempra” and, eager to learn more, he asks Hermione if she’s familiar with it. She immediately rebukes him, insisting that anyone with any sense of self-respect would have turned the book in by now. Despite her disapproval, Harry continues to immerse himself in the annotated pages, growing more obsessed with the book and showing no interest in uncovering the identity of the mysterious Half-Blood Prince.
As Harry excels in Potions, much to his delight, Hermione—who’s always prided herself on her academic skills—begins to feel a twinge of jealousy. When Harry refuses to let her take a look at the book, Ginny Weasley steps in, snatching it from his hands and revealing that it belongs to the Half-Blood Prince. Though Harry insists he wants to know more about the book’s previous owner, his actions suggest otherwise, as he remains focused on perfecting his potion-making rather than solving the mystery. Later, Hermione confesses that she has searched the library, hoping to find any mention of the Half-Blood Prince, but with no luck.
In Harry Potter and the Half-Blood Prince, Chapter 24, titled “Sectumsempra,” Harry discovers a spell labeled “For Enemies” in the Half-Blood Prince’s potions book. Initially unsure of its exact effects, Harry is drawn to the spell simply because of the label. Later, during a confrontation with Draco Malfoy in the boys’ bathroom, Harry decides to try it out. With no clear understanding of what the spell actually does, Harry shouts “SECTUMSEMPRA!” as he aims his wand at Draco.
The result is immediate and terrifying: Draco collapses, his chest and face bleeding heavily as though he’s been slashed by an invisible sword. Horrified, Harry realizes the gravity of his mistake. Moaning Myrtle, who witnesses the entire scene, screams, alerting Severus Snape. Snape rushes in, performs a series of incantations, and manages to stop Draco’s bleeding. He tells Draco to go to the hospital wing and orders Harry to stay behind, clearly upset by the severity of the situation.
Snape is the creator of Sectumsempra
The Sectumsempra curse is a brutal spell that causes deep, painful slashes and severe bleeding. In Harry Potter and the Half-Blood Prince, Harry argues that he never intended to seriously harm Draco and had no idea about the spell’s full effects when he used it. After Snape questioned Harry about the incident, he sentenced him to detention every Saturday for the remainder of the school year.
Hermione, on the other hand, was appalled by the spell’s use and questioned the ethics of the book’s former owner, the Half-Blood Prince. Ginny, however, took Harry’s side, seeing his actions as justified self-defense, particularly because Draco had just tried to cast the Cruciatus Curse on him. Ginny appreciated that Harry had a powerful spell to protect himself, while Hermione was frustrated by the mess Harry had gotten into by using it.
As Harry Potter and the Half-Blood Prince reaches its climax, Snape finally reveals his true identity as the Half-Blood Prince. This shocking disclosure occurs after he kills Dumbledore with the Avada Kedavra curse and flees the castle, accompanied by Bellatrix, Draco, and several others. Harry, unaware that Dumbledore had actually arranged his own death with Snape, is consumed by rage and heartbreak. He pursues Snape and confronts him near Hagrid’s Hut. In his fury, Harry casts the Incarcerous spell to bind Snape, demanding that he fight back, but Snape easily deflects it.
Harry, mustering his last ounce of strength, pushed himself to his feet and shouted, “Sectumsempra!” But once more, Snape easily deflected the spell and moved in closer, his tone dripping with disdain as he said, “You dare use my own magic against me, Potter? Yes. I am the Half-Blood Prince.” It was then that the truth came to light: the annotated Advanced Potion-Making book Harry had been using had belonged to none other than Severus Snape during his years at Hogwarts. Additionally, Snape himself had created the Sectumsempra curse, designing it specifically to target his enemies—particularly the Marauders, who had relentlessly bullied him while they were all students at the school.