Situated at the heart of a rapidly gentrifying district of Seoul, the Yeonnam-dong Smiley Laundromat is a place where the extraordinary stories of ordinary residents unfold. It is already a haven of tranquility and reflection for locals, but when someone leaves a notebook behind, the laundromat becomes a place that brings people together. One by one, customers start jotting down candid diary entries, opening their hearts and inviting acts of kindness from neighbours who were once just faces in the crowd. But there is more to the diary than first appears, and before long the laundromat's regulars are teaming up to solve a mystery and help the notebook's former owner find peace.