In the cozy house of husband Samuel and wife Sirena, Muffin the cat and Duncan the mouse are constantly at odds, engaged in a never-ending game of chase and traps. But their lives take an unexpected turn when Samuel brings home a surprise guest, a large dog named Diamond, entrusted to him by their neighbor for the summer.

Diamond's arrival disrupts the house's delicate balance, instilling fear in both Muffin and Duncan. Determined to regain control over their home, the unlikely duo stumbles upon a magical potion that grants them the ability to understand each other's language.

As Muffin and Duncan spend time together, they realize that their differences are not as significant as they once believed. United by their shared desire to reclaim their territory, they form an alliance and devise a plan to teach Diamond a lesson he won't soon forget.

With their newfound friendship and clever tricks up their sleeves, Muffin and Duncan outwit Diamond at every turn. Together, they transform the house into a maze of surprises, setting traps that leave Diamond bewildered and eager to return to her own home.