Zhao Dashan buys a four-yuan pack of cigarettes on his late wife Sufen's birthday and is publicly humiliated by his son Zhao An and daughter-in-law Li Ran, so he angrily moves back to the old family house on Locust Tree Lane. The couple then discovers the truth: the old man spent his life savings to buy them a home and used his entire pension to pay off the mortgage and support the household, leaving them consumed with guilt. When their granddaughter Xinxin is suddenly diagnosed with leukemia, the old man resolutely sells the house to save her and drives off relatives who come to seize the property. In the end, Xinxin recovers, the old man returns to the old house to live out his years in peace, his children finally grow up, and the family finds its own modest share of happiness, each with their own smoke and fire of home.