Shortly after the mouse family settles in America, they discover they still face threats from cats. This makes them eager to try moving to a new home in the West, where it is promised that mice and cats can coexist peacefully. Unfortunately, the one making this promise is a smooth-talking con artist named Cat R. Waul, who actually harbors sinister intentions. Unaware of this, the mouse family embarks on their journey westward, while their true cat friend Tiger follows closely behind, determined to pursue his girlfriend who has left in the same direction.