Fievel is a young Russian mouse separated from his parents on the way to America, a land they think is without cats. When he arrives alone in the New World, he keeps up hope, searching for his family, making new friends,…

故事发生在一群被NIMH（国家智能研究中心）的小老鼠身上，人们利用这些老鼠进行智力开发之类的实验。实验进展得很顺利，老鼠们都有了类似人类的智商，于是他们计划出逃，但是在此过程中一位勇敢的老鼠牺牲了.....