Activists set lab animals free from their cages--only to learn, too late, that they're infected with a "rage" virus that turns them into frothing, savage killers. The virus quickly spreads to human beings, and when a man named Jim (Cillian Murphy) awakens in an empty hospital and walks outside, he finds a deserted London. In a series of astonishing shots, he wanders Piccadilly Circus and crosses Westminster Bridge with not another person in sight, learning from old wind-blown newspapers of a virus that turned humanity against itself. Advertisement So opens "28 Days Later," which begins as a great science fiction film and continues as an intriguing study of human nature. The ending is disappointing--an action shoot-out, with characters chasing one another through the headquarters of a rogue Army unit--but for most of the way, it's a great ride. I suppose movies like this have to end with the good and evil characters in a final struggle. The audience wouldn't stand for everybody being dead at the end, even though that's the story's logical outcome.