Tricky business, playing the wife who is cheated on by a movie's hero. If you go too shrill and harpyish, you give the audience a chance to excuse him. If you play the victim, you give the audience a chance to hate him. Either way, it takes away from the tragedy.
Michelle Williams, 25, best known for TV's three-alarm teen weepie Dawson's Creek, gets it just right. When she sees her husband in a hungry kiss with another guy, she registers that horror-queasiness of having something she couldn't articulate become terribly clear. "Without her, this movie wouldn't work," says co-star Jake...