The story follows Harry's sixth year at Hogwarts as he receives a mysterious textbook, falls in love, and attempts to retrieve a memory that holds the key to Lord Voldemort's downfall.

Lord Voldemort tightens his grip on the wizarding and Muggle worlds: his Death Eaters kidnap Mr Ollivander, a Wand maker and destroy London's Millennium Bridge.

Draco's mother, Narcissa, and aunt Bellatrix Lestrange seek out Severus Snape, who gains their confidence by claiming he is a mole within the Order of the Phoenix.

Ron makes the Gryffindor Quidditch team as Keeper and begins dating Lavender Brown, upsetting Hermione, who harbours feelings for him.

His suspicions about Draco are dismissed by the Order, but Arthur Weasley reveals that the Malfoys may be interested in a Vanishing Cabinet at Borgin & Burke's.

In Hagrid's hut, Harry uses his Liquid Luck potion to convince the reluctant Slughorn to surrender the memory Dumbledore needs.

Viewing it in the Pensieve, Dumbledore and Harry learn Voldemort sought information about Horcruxes, magical objects containing pieces of a wizard's soul for immortality.

A weakened Dumbledore defends them from Inferi by creating a ring of fire, and apparates them back to Hogwarts, where Bellatrix, Greyback, and other Death Eaters have entered through the Vanishing Cabinet in the Room of Requirement that Draco has secretly connected to one in Knockturn Alley.

As Hogwarts students and staff mourn Dumbledore's death, Harry tells Ron and Hermione that the locket is fake and contains a message from "R.A.B.

[10][11] Emma Watson considered not returning for the film, citing fear of being typecast, but eventually decided that "the pluses outweighed the minuses" and could not bear to see anyone else play Hermione.

[20] Thomas James Longley was the original choice to take on the role, but Riddle was ultimately played by Hero Fiennes-Tiffin as a child and Frank Dillane as a teenager.

[45] On the weekend of 6 October 2007, the crew shot scenes involving the Hogwarts Express in the misty and dewy environment of Fort William, Scotland.

However, since the screenplay required a snowy atmosphere for the train to go through and it did not snow during planned production dates, the crew decided to film these scenes in Rauma Line, Norway.

[51][52][53] Due to cinematographer Bruno Delbonnel's use of de-focussing and soft wipes in the digital grade, Warner Bros. asked director David Yates to add more colours to the film.

In an interview with the Academy, Delbonnel said that he did not want to change the lighting effects used in the previous films, and finally decided to give it a darker, moody variation of grey.

"[57] The opening scenes of the Death Eaters' attack on Diagon Alley and London was created by Double Negative, led by VFX supervisor Paul Franklin.

Double Negative spent six months surveying and documenting the environment around the River Thames and Trafalgar Square to create the swooping views of the city.

Double Negative also contributed to the Pensieve sequences, developing complex directed fluid simulations to realise the swirling world of memory and the past.

[70] The special-edition two-disc DVD for Harry Potter and the Order of the Phoenix contained two sneak peeks of the film, while the US edition included an additional clip.

[88] Warner Bros. executive Alan F. Horn noted that the move was meant "to guarantee the studio a major summer blockbuster in 2009," with other films being delayed due to the 2007–08 Writers Guild of America strike.

[93] The date change was met with a heavily negative reaction by Harry Potter fans, as the Los Angeles Times noted: "Petitions were circulating, rumors were flying and angry screeds were being posted on Internet sites within minutes of the Thursday announcement.

Despite each being owned by Time Warner Inc., Entertainment Weekly was unaware of the change until it was publicly announced by WB and noted that readers would now be in possession of a "Dewey Defeats Truman collectible".

[94] Following the date change, Half-Blood Prince's release slot was taken by Summit Entertainment's Twilight and Walt Disney Pictures' Bolt.

[102] The Blu-ray and DVD include an 11-minute, 38-second feature on the new Wizarding World of Harry Potter mini theme park, which opened on 18 June 2010 at Islands of Adventure in Orlando, Florida.

The website's critical consensus reads, "Dark, thrilling, and occasionally quite funny, Harry Potter and the Half-Blood Prince is also visually stunning and emotionally satisfying.

He commented, "Harry Potter and the Half-Blood Prince is a tour-de-force that combines style and substance, special effects and heart and most importantly great performances from all of the actors young and not-so-young".

He praised Alan Rickman's performance, described Helena Bonham Carter as "mesmerising", and Jim Broadbent as a "grand eccentric old professor".

[144] BBC News's Tim Masters praised the film's cinematography, visual effects, production design, acting and darker plotline.

[148] Screen Daily commented, "David Yates and his team struggle to whip J.K. Rowling’s 608-page tome into a consistently thrilling cinematic experience", but praised the shooting of some scenes and Bonham Carter's acting.

[150] The film was nominated for BAFTA Awards in Production Design and Visual Effects,[151] and was in the longlists for five other categories, including Best Supporting Actor for Alan Rickman.