In a quiet countryside village lies an ancient, family-owned hot spring, passed down through generations. As it prepares for its grand reopening, Jinho is suddenly left to run the bathhouse alone. His only help? Sejeong, the gorgeous girl next door. As they work together to deep-clean the place, they stumble upon a mysterious bundle of herbs and an old medicinal book in the storage room. When they brew a vibrant, green herbal bath from the fragrant herbs, something unexpected begins to heat up—and it’s not just the water!