Chaos theory teaches us that small events can have enormous consequences. An opening title informs us that butterfly flapping its wings in Asia could result in a hurricane halfway around the world. Yes, although given the number of butterflies and the determination with which they flap their little wings, isn't it extraordinary how rarely that happens? "The Butterfly Effect" applies this theory to the lives of four children whose early lives are marred by tragedy. When one of them finds that he can go back in time and make changes, he tries to improve the present by altering the past.