For the sixth and third-to-last time, we enter J.K. Rowling’s enchanting cinematic realm of magic and mischief. But a new and sinister fog looms heavily over “Harry Potter and the Half-Blood Prince.” From the film’s opening scenes, in which Death Eaters whiz by like toxic, black fumes across Britain’s bright skies and cause chaos throughout London, the malevolence that will characterize the rest of the Potter series becomes painfully evident. Although this installment works largely as a transition for the two-part finale, the strengths of David Yates’ directing and Steve Kloves’ script make this Potter film the strongest and most entertaining to date.

In “Half-Blood Prince,” Voldemort is back and more powerful than ever. In addition to wreaking havoc throughout both muggle and wizarding worlds, the Dark Lord has entrusted the young Draco Malfoy with a daunting assignment that endangers the lives of multiple characters throughout the school year. Voldemort’s most formidable opponent, Headmaster Albus Dumbledore, has begun to show signs of increasing fragility, ominously symbolized by his injured hand. Hogwarts, once seen as a rare safe haven, begins to lose much of its structural integrity.

Despite the film’s grim tone, the storyline isn’t all danger and darkness. After a two-year absence, Quidditch is back, and Ron Weasley (Rupert Grint) joins the Gryffindor team as Keeper. Comic relief comes in the form of new characters, most notably Ron’s annoyingly perky girlfriend Lavender Brown (Jessie Caves) and the arrogant Cormac McLaggen (Freddie Stroma), who compulsively chases after Hermione Granger (Emma Watson). Both in and out of the classroom, the Potter characters learn to brew love potions as relationships foment between Ron and Hermione as well as Harry and Ginny.

The acting in “Half-Blood Prince” is at its series peak. Although greatness can be expected from the giants of British acting that appear throughout the film—Alan Rickman as Snape, Michael Gambon as Dumbledore, Helena Bohman Carter as Bellatrix Lestrange, among others—the most surprising depth is seen in the younger actors, especially Watson and Tom Felton, who plays Draco. The inner turmoil caused by his burdensome task allows Felton to express a broader range of emotions than in previous films.

Potter fans searching for a close adaptation of the sixth book should steer clear of “Half-Blood Prince.” Kloves has exercised more artistic freedom than ever in this film, cutting memorable storylines (including trips through the pensieve to Voldemort’s tragic childhood and family history), and introducing entirely new scenes (such as when the Death Eaters attack the Weasleys’ home). But overall, Kloves’ changes contribute to a much more compact film; “Deathly Hallows” is the first in the series to progress at an adequate pace rather than at the speed of a Golden Snitch.

Although the Potter films continue to mature in both quality and subject matter, now catering more toward adult audiences, the saga will remain emblematic of an entire generation’s childhood. On July 15th, 2011—the release date of the eighth and final film, “Harry Potter and the Deathly Hallows”—these fans will greet the theaters with mixed emotions as the series comes to an epic conclusion, simultaneously marking their unofficial induction into adulthood.

—Staff writer Andres A. Arguello can be reached at arguello@fas.harvard.edu.