The film opens with Death Eaters wreaking havoc in both the magical and Muggle worlds. Albus Dumbledore (played by Michael Gambon) arrives at Privet Drive to collect Harry Potter (played by Daniel Radcliffe) and take him to The Burrow, the Weasley family’s home. Harry is informed that Voldemort is terrorizing both the wizarding and Muggle worlds, and Dumbledore asks for Harry’s help in convincing former Potions Master Horace Slughorn (played by Jim Broadbent) to return to Hogwarts.
Back at Hogwarts, Professor Severus Snape (played by Alan Rickman) is appointed as the Defense Against the Dark Arts teacher, while Professor Slughorn takes over as Potions Master. Dumbledore and Harry spend time together, visiting memories stored in a Pensieve to learn more about Voldemort’s past and his quest for immortality.
Meanwhile, Ron Weasley (played by Rupert Grint) begins dating Lavender Brown (played by Jessie Cave), much to Hermione Granger’s (played by Emma Watson) dismay. Harry becomes infatuated with Ron’s sister, Ginny (played by Bonnie Wright), but keeps his feelings to himself.
As the year progresses, Dumbledore reveals to Harry that he has found one of Voldemort’s Horcruxes, objects containing pieces of his soul that must be destroyed to weaken him. Together, they set out to retrieve it, but are ambushed by Death Eaters. Dumbledore is fatally cursed by a Horcrux-infused potion, and Severus Snape appears and kills him. Draco Malfoy (played by Tom Felton) hesitates to kill Dumbledore when given the opportunity, but Snape ultimately carries out the deed.
In the chaos following Dumbledore’s death, the Death Eaters invade Hogwarts, but Harry, Ron, and Hermione manage to escape. They vow to find and destroy the remaining Horcruxes, while the wizarding world falls under Voldemort’s control.
The film ends with Harry, Ron, and Hermione preparing to embark on their quest to find the Horcruxes, knowing that their journey will be perilous and fraught with danger.
“Harry Potter and the Half-Blood Prince” is a dark and emotional installment in the series, setting the stage for the climactic battle between Harry and Voldemort in the final films.