Giant spiders from the Forbidden Forest enter the school, fighting on the side of the Death Eaters, as Harry, Ron, and the Weasleys try to move Fred’s body to a safe place. Ron wants to stay and fight to avenge his brother, but Hermione urges him to focus on the goal: to destroy Nagini, the last known Horcrux. Harry uses his ability to see through Voldemort’s eyes to find out where he is, and has a vision of Voldemort in the Shrieking Shack in Hogsmeade ordering Lucius Malfoy, who is frantic with worry about Draco, to go fetch Snape.
They head toward the Whomping Willow to enter the passageway to the Shrieking Shack, on the way fighting off attacking Death Eaters and saving Draco Malfoy’s life from a Death Eater who mistakes him for an enemy. Before they reach the Willow, they see that giants have joined the fight on both sides, and they have to fight off a hundred dementors, with some help from Luna, Ernie, and Seamus, who have mastered the art of summoning Patronuses.
Harry, Ron, and Hermione enter the passage and creep to where they can observe what’s happening in the Shrieking Shack. Voldemort is telling Snape that the Elder Wand is working no better than his old wand and has not given him the extraordinary powers it was supposed to. Voldemort concludes that he is not yet the true master of the Elder Wand, because Snape killed its previous owner, and thus Voldemort must kill Snape to be the wand’s master. Voldemort orders Nagini to kill Snape, and the great snake bites Snape’s neck, mortally wounding him. Voldemort leaves.
Harry goes to Snape’s body, and Snape, dying, tells Harry to “Take it,” and expels a silvery substance from his mouth, nose, and ears. Harry collects the substance in a flask that Hermione provides, and Snape, after telling Harry to look at him, dies.
Voldemort addresses the school, telling them that he will give them a one-hour reprieve to dispose of their dead and treat the wounded. He announces that Harry should meet him alone in the Forbidden Forest in one hour, or Voldemort will recommence the battle, enter the fray himself, and kill every person who helped Harry.
In the Great Hall of Hogwarts, those who have died fighting for Harry are laid out. Among the dead are Lupin and Tonks.
Leaving behind his grieving friends, Harry goes to Dumbledore’s office to place Snape’s memories into the Pensieve for viewing, witnessing Snape’s true life story. He sees Snape as a boy of nine or ten, observing Lily Evans, Harry’s future mother, first discovering her magical talents, and Snape clumsily trying to befriend her by telling her about her true nature as a witch. In a slightly later memory, Snape has become her friend and is giving Lily her first introduction to the wizarding world. Lily’s sister, Petunia, taunts Snape for his awful clothes, provoking him into attacking her, which angers Lily.
Harry observes a scene in which Snape watches Lily say good-bye to her family to board the Hogwarts Express for the first time. Lily reveals to Petunia that she knows that Petunia, who professes to hate magic, begged Dumbledore to admit her to the school. Petunia angrily accuses Lily of being a freak and a sneak, and Lily feels discomfort regarding Snape, who was the one who stole Petunia’s letter of response from Dumbledore. On the train, young James Potter and Sirius Black taunt and mock Snape.
Harry sees Snape’s disappointment at Lily’s being Sorted into Gryffindor rather than his own Slytherin. Later in their school career, Lily and Snape are still close friends, but Snape is jealous of James Potter’s attraction to her, and Lily disapproves of Snape’s Dark magic–practicing friends. Lily is furious with Snape for calling her a Mudblood, and for speaking contemptuously of Mudbloods in general. Snape frantically apologizes, but Lily tells him they have chosen separate ways.
Harry watches as Snape meets with Dumbledore on a wild hilltop. Snape has sworn loyalty to Voldemort but is meeting with Dumbledore secretly because he knows that Voldemort plans to kill Lily, her husband James, and her son, all because Snape told Voldemort about Professor Trelawney’s prediction that Voldemort would be killed by a boy born at the end of July. Snape promises to do anything Dumbledore asks if he will protect Lily.
Later, in Dumbledore’s office, Snape sobs for Lily Potter’s death. Dumbledore tells him that the son survived, and that Snape’s path is clear if he truly loved Lily. Snape agrees to devote his life to protecting Harry but makes Dumbledore promise never to tell anyone.
Much later, when Harry is a student at Hogwarts, Snape expresses his irritation at how Harry resembles his father in attitude and actions. Still later, Dumbledore and Snape discuss Karkaroff’s darkening Dark Mark, and Voldemort’s imminent return, which it presages.
In another memory, Snape ministers to Dumbledore after Dumbledore rashly puts on the ring of Marvolo Gaunt and suffers a blackened and burned hand because of the ring’s curse. Snape’s potions buy Dumbledore a year of life, but nothing they do can prevent the curse from killing him eventually. Dumbledore makes Snape promise to protect the students at Hogwarts if Voldemort gains control of the school, to help Draco stay out of trouble as he tries to carry out Voldemort’s instructions to kill Dumbledore, and to kill Dumbledore himself when the right time comes.
Later, Dumbledore tells Snape that after Snape kills Dumbledore, there may come a time when Voldemort seems to fear for the life of his snake (which will mean that the other Horcruxes are destroyed or threatened). At that moment, Snape should tell Harry the truth: that when Voldemort sent his killing curse at Lily Potter and blasted his own soul to bits, a piece of Voldemort’s soul bound itself to Harry’s. This event is the reason that Harry can read Voldemort’s mind and can speak Parseltongue. As long as Harry lives, so will Voldemort. The only way Voldemort will die is if all of the Horcruxes are destroyed and Voldemort himself kills Harry, who is in fact the seventh Horcrux. Snape is furious, accusing Dumbledore of raising Harry as a lamb for slaughter and using Snape by falsely telling him he was protecting Lily Potter’s son.
Later, after Dumbledore’s death, the portrait of Dumbledore tells Snape to give Voldemort the correct date of Harry’s departure from the Dursleys and to plant the idea of using decoys, so Harry can escape. In the pursuit of Harry, Snape burns off George Weasley’s ear accidentally, while trying to protect Lupin from a Death Eater.
Snape goes to Sirius’s house and steals the small fragment at the end of the letter Harry found, simply because the page is signed “Lots of love, Lily.” He tears Lily’s picture out of the photograph of Lily, James, and Harry.
Finally, the portrait of Phineas Nigellus tells Snape that Harry and Hermione are hiding in the Forest of Dean, Hermione having mentioned the place while opening her magic bag. Dumbledore urges Snape to take the Sword of Gryffindor to them under the right conditions, and Snape leaves, on his way to put the sword under ice and use his own Patronus (the silver doe) to guide Harry.
The memories over, Harry wakes up in the headmaster’s office.
Snape has no chance to fight or stand up to Voldemort, and thus has no time to demonstrate his true heroic character before he dies. His final actions are as tightly cloaked in mystery as everything he has done throughout the series. Sadly, his death accomplishes nothing, as Voldemort is simply pursuing one more misguided and doomed scheme to acquire the power to beat Harry. Fortunately for Harry, Snape has time for one last act, extracting his memories for viewing in the Pensieve, the headmaster’s privilege (since the Pensieve is in the headmaster’s office).
The viewing of Snape’s life story in the Pensieve is very satisfying, as it explains everything mysterious or contradictory that we have witnessed about Snape throughout the series. His connection with Slytherin and past as a Death Eater are all real, but his animosity toward Harry was never malice, but simply irritation at seeing Harry’s father reflected in him. We knew since Harry Potter and the Prisoner of Azkaban that Harry’s father had persecuted Snape, but we never saw that Snape’s hatred of James Potter was counterbalanced by a much stronger emotion. Much to our surprise, everything that Snape has ever done throughout the series has been motivated by love. The sudden revelation that things were not as they seemed, and that something else was going on all along that we are only now aware of, is called irony, and it is one of the most pleasurable experiences an author can produce. When the events in question concern a character who has fascinated us and held our attention through seven books, the experience for the reader is rare and special.