When you've followed Buffy for a while, you'll notice that once or twice a season the producers like to stir things up - like a small boy poking a stick into an ant's nest. This two-part story is outstanding. By the end of it there's hardly a character whose life hasn't undergone some emotional turmoil or a dramatic upheaval.

Whedon's script, which ruminates on friendship, loyalty, trust and betrayal, has beautifully honed dialogue, and exhibits his customary command of the dynamic relationships between the lead characters.

Angel's reversion to the dark side is a wholly welcome dramatic masterstroke, and introduces some tantalising sexual rivalry between Spike and Angel for Drusilla's affections. As the revitalised Angel David Boreanaz is finally given something more to do than mope about looking sulky, and makes the threat he now poses to Buffy seem quite tangible: "She made me feel like a human being. That's not the kind of thing you just forgive�"

It's Juliet Landau as Drusilla who steals the show, though, with a mesmerising portrayal of madness. There's a magical moment when she tells Spike she's named all the stars: "But I've named them all the same name, and there's terrible confusion�"

If there's one disappointing aspect to Innocence, it's that The Judge, whose ominous reputation had been trumpeted throughout Surprise, turns out to be a rather impotent villain, and this deflates some of the episode's power. The way he is dispatched, though, is satisfying, and amusingly confounds the audience's expectations.