Nine-year-old girl Dou Dou, in order to raise medical expenses for her mother, unexpectedly discovers a preserved old fifty-yuan bill from ten years ago, and the handwriting on it is surprisingly identical to a letter left by her father. Following this old banknote and half a copper button, she gradually uncovers her own family background, and also allows a family secret sealed for many years to resurface. Barbecue stand owner Long Ye, due to a kind action, accompanies the mother and daughter all the way to search for the truth. Family affection, guardianship, and promises intertwine, and a path of reunion spanning ten years thus unfolds.