In a cozy cheese factory lives a family of gray mice, enjoying a warm home and settled life with their well-behaved son. But everything changes when a family of white mice moves in, bringing tension and a "mouse war" of Shakespearean drama.

The gray and white parents’ hostility grows, while their children, oblivious to the feud, like each other and long to be friends. Courageously, they set off to seek help from the Great Cat, hoping to bridge the divide between their families.