Guest is a mouse who had built a secret nest in Yuna's studio apartment, living peacefully while pilfering food. However, that peace did not last long.

Yuna discovers traces of the mouse living in the house and, as a drastic measure, adopts a fearsome(?) stray cat named 'Godeungeo'! Furthermore, Yuna's friend Hyunwoo begins staying at the apartment, armed with all sorts of mousetraps and capture equipment.

Yuna's sharp screams, Hyunwoo's clumsy tactics, and the persistent pursuit of Godeungeo—who acts cute in front of humans but turns into a predator when they are alone—begin. Guest must overcome the narrowing territory and survive in this dynamic studio apartment!