No need to spike the Diet Coke with Felix Felicis, the formal name of liquid luck.

"Harry Potter and the Half-Blood Prince" has all the ingredients for a perfect potion: A source book many consider their favorite, a successful franchise, a cast of old friends, the felicitous addition of actor Jim Broadbent, a proper dose of humor, budding romances and black-hearted betrayal.

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'Harry Potter and the Half-Blood Prince'

3 1/2 stars = Very good
Ratings explained

• Starring: Daniel Rad­cliffe, Michael Gambon, Rupert Grint, Emma Watson.
• Rating: PG for scary images, some violence, language and mild sensuality.
• Web site: http://harrypotter.warnerbros.com/

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"Half-Blood Prince" is faithful to the J.K. Rowling novel but those who read it may find themselves with a touch of phantom pain, missing what's not there. Key backgrounds, battles, hospitalizations and even house elves get short shrift.

Professor Dumbledore (Michael Gambon) speaks for many in the audience when he's struck by the fact that Harry (Daniel Radcliffe) needs a shave after a long day. "At times I forget how much you've grown," he says with grandfatherly tenderness.

He still sees Harry as the boy who came to the Hogwarts School of Witchcraft and Wizardry as an 11-year-old orphan. Now, he and his mates are 16 and, as another professor says of Harry, Ron Weasley (Rupert Grint) and Hermione Granger (Emma Watson), "Why is it when something happens, it is always you three?"

As the story opens, the Death Eaters are casting inky, murderous shadows over the Muggle and wizarding worlds.

They leave a fiery trail after swooping through shops, twist London's Millennium Bridge like double Dutch jumping ropes, and convince Harry that classmate Draco Malfoy (Tom Felton) totally has thrown in with the dark side and is plotting against him.

Upon his return to Hogwarts, Harry is enlisted in Dumbledore's efforts to capture and review memories that will allow them to understand the evil Lord Voldemort. A prophecy about Harry and Voldemort, "Neither can live while the other survives," haunts the boy wizard.

Not everyone is enamored of Harry's status, as the sour Professor Snape (Alan Rickman) suggests with dripping sarcasm, "How grand it must be to be 'the chosen one.' "

Dumbledore has rehired a potions professor, Horace Slughorn (Broadbent), who may hold a key to Voldemort's power. Slughorn is the faculty equivalent of a celebrity-seeker, perfectly in keeping with our times, and is happy to befriend Harry.

At the same time, Harry has discovered an annotated potions book that belonged to an unknown "Half-Blood Prince" and is helping him to ace his class. Like many lovestruck teens, he is pining for a classmate who comes with complications, while Ron is mooning around (sometimes thanks to a potion) and Hermione steaming over the "snogging" or serious kissing going on.

As readers of the book know, the movie builds to the death of a beloved character and sets the stage for events of the seventh and final book, so dense and long that it's being turned into a pair of movies.

David Yates, who directed 2007's "Harry Potter and the Order of the Phoenix," returns along with screenwriter Steve Kloves. With director of photography Bruno Delbonnel, they paint with color, light, shadows and detail, all the while relying on the familiar music to instantly transport us to this magical world.

"Harry Potter and the Half-Blood Prince" deals with characters who lose their souls, those who struggle with what they see as their frightful fate and others who pledge their allegiance to friends and mentors.

As a wise wizard says to an attacker: "Years ago, I knew a boy who made all the wrong choices. Please let me help you."

The core cast is as rock solid as ever, although time for Robbie Coltrane as Hagrid and Rickman, especially, seems truncated. Broadbent, who contorts his face in a wonderfully quirky way, can appear dotty or sycophantic and is an excellent addition.

Some passages of the book, such as those dealing with an engagement that tests a couple's mettle and love, have been eliminated, while others that better explain the bad seed Tom Riddle (who would become Voldemort) are hinted at, rather than dramatized.

The movie ends on as sunny and hopeful a note as possible but parents should take the PG rating seriously. Creatures who arise in the darkness are frightening, although a key death that I thought would reduce the audience to audible sniffles did not, at least at the preview I attended.

I was happy to have read this rich book, so I could fill in the many gaps, but as a movie, it works like a well-cast spell or expertly brewed potion. Even at 151 minutes, it leaves you wanting more.