Near the end of "Harry Potter and the Chamber of Secrets," Professor Albus Dumbledore, the headmaster of Hogwarts, announces to the students that in honor of the wonderful work done by Harry and his friends Rupert and Hermione, the year's final tests will be cancelled. Everyone cheers: "Yes!" and then there is a cutaway to a closeup of Hermione, the perfect student, silently and sadly mouthing to herself "Oh, no…." It's one lovely moment among many in this Episode II of the J.K. Rowling series.

The question on everyone's mind is how this compares with last year's "Sorcerer's Stone," and the answer is it is better, richer, and more confident of itself; but it is also more conventionally structured as a thriller rather than an adventure, and at two and a half hours it is also about fifteen minutes too long for its own good. Particularly in the final half-hour, which is set in the actual Chamber itself, the plot line is too thin to sustain the repeated shocks of fear that director Chris Columbus keeps putting into the frame.

Nevertheless it perfectly honors Rowling's vision, and reminds us again that these films are a miracle of casting. We start with the three children - Daniel Radcliffe as Harry, Rupert Grint as Ron, and Emma Watson as Hermione. They have taken their characters off the page and put them, very much alive, onto the screen in a way that now makes the books simply printed versions of the films. They are expressive (Grint sometimes a bit too much so), unselfconscious in their line readings, and transparent to the camera and therefore to us. We can actually read their minds.

And once again the adults are superb, including the new character of the charlatan wizard Gilderoy Lockhart (Kenneth Branagh) and Draco Malfoy's father Lucius (a particularly slimy performance by Jason Isaacs, with his ash-blond ponytail and supercilious smirk). Richard Harris, as Dumbledore, sadly shows signs of his impending death; he is weak and light-voiced, he does not move in front of the camera, and his face sags well down into his long beard. But everyone else at Hogwarts remains at the top of their form.

The story itself is quite thin, a slight failure of imagination for Rowling; it's as though she suffered a sophomore jinx after the spectacular richness of the first book. Not much actually happens in this one, which turns out to be a bonus for the movie, for it gives Columbus more space and time in which to open up his scenes. The requisite quidditch game is longer, and the game's final chase between Harry and Draco even ends up a cross between "Ben-Hur" and "Star Wars." And one charming feature of the film is that the secret of the Chamber of Secrets is to be found in the middle of the girls' bathroom, shown stalls, toilets, sinks and all. No bowdlerization here.