Slughorn knows crucial information about the world-ending dark lord, Voldemort, who killed Harry’s parents and whom we get to see, courtesy of a vial containing his memories when he was a mean young Hogwarts student named Tom Riddle. Professor Dumbledore (Michael Gambon) recruits Harry (Daniel Radcliffe) to get the professor to open up. Harry’s proficiency at making a “living death’’ potion makes Slughorn easier to charm; Harry happens to be using an old textbook that, according to an inscription once belonged to someone called the Half-Blood Prince.
Meanwhile, the young, moody, and acutely blond Draco Malfoy (Tom Felton) begins his stint as Voldemort’s recruit to assassinate Dumbledore, with the secret backing of Professor Severus Snape (Alan Rickman, as deliciously reptilian as he always is in these films).
There’s a biblical tinge to some of this, even if most of these movies feel interchangeable with Peter Jackson’s “Lord of the Rings’’ trilogy. Partly, it’s because Gambon’s Dumbledore - with his long white hair and matching, scrunchied beard - looks like Moses by way of George Clinton and Gandalf the White. At some point, Gambon uses a staff to part an infernal red sea, which I think I’ve seen Clinton do.
Steve Kloves has written five of the “Harry Potter’’ screenplays, and “The Half-Blood Prince’’ reeks of formula. An hour or so of interesting character development followed by 30 minutes of boredom, then an hour of plot development. That second hour always feels as if Kloves just remembered that he has to lay the groundwork for the subsequent movie. The individual installments become extensions on a lengthening fuse.
