“Thank you for knocking on my door.” Near future in Seoul, Oliver and Claire are abandoned helper robots stuck in a rut. One day, Claire knocks on Oliver’s door to borrow a charger and they grow closer since then. Oliver hoping to meet his former owner again and Claire dreaming of seeing fireflies, the two decide to leave for Jeju Island. During the unexpected journey, they end up finding themselves falling in love. However, the joy of love soon fades away as Claire helplessly breaks down. With sad ending waiting for them, the two robots learn what love can bring.