艾雲對不愉快的童年印象模糊，失憶令他在困擾中成長。兒時心理醫生著他保存的生活筆記，和青梅竹馬的摯友姬莉、連尼及湯美，是他對往事的僅餘線索。十數年後，艾雲意外地發現筆記簿可帶他回到過去。艾雲知道要擺脫夢魘，一定要改寫過去，他孤注一擲，決定借童年的自己，扭轉今日的命運。 然而，當艾雲每次在「過去」改變歷史，「現在」的境況也會一同變異，仿似物理現象的連鎖反應──不可思議的「BUTTERFLY EFFECT」，令情況越變越壞，竟致一發不可收拾。

A mathematical genius discovers a link between numbers and reality, and thus believes he can predict the future.

In Seattle, detective Quentin Conners is unfairly suspended and his partner Jason York leaves the police force after a tragic shooting on Pearl Street Bridge, when the hostage and the criminal die. During a bank heist with a hostage situation, Conners is assigned in charge of the operation with the rookie Shane Dekker as his partner. The thieves, lead by Lorenz, apparently do not steal a penny from the bank. While chasing the gangsters, the police team disclose that they planted a virus in the system, stealing one billion dollars from the different accounts, using the principle of the Chaos Theory. Further, they find that Lorenz is killing his accomplices.

Chaos theory has a bad name, conjuring up images of unpredictable weather, economic crashes and science gone wrong. But there is a fascinating and hidden side to Chaos, one that scientists are only now beginning to understand. It turns out that chaos theory answers a question that mankind has asked for millennia - how did we get here?