The story tells of 34-year-old Takuma Omagi’s journey back from a midlife crisis in which he suffered a mental breakdown due to overwork, lost his position in society, and was abandoned by his wife. While Takuma is convalescing at home, he discovers a key left behind by his father, who died five years earlier. It’s the key to an old truck, number BT21, that once belonged to the Soma Trucking Company. The narrative subsequently moves back and forth between the year 2000, Takuma’s present, and 1963, when his father, Shiro, worked for Soma Trucking.
In the 1963 time frame, Shiro is concerned about Soma Trucking’s unsteady bottom line, and he attempts to diversify the company by launching a home delivery service. Obstructive actions by the yakuza Narusawa make the new venture unviable, however, and the company goes belly-up. The narrative describing this process involves a complex web of relationships between loan officer Atsushi Sakuraba at Mitsuba Bank, the president of the trucking company, the driver of BT21 who is forced to work for Narusawa as security for a loan, and many others.
In the present, Takuma unravels Shiro’s past as he attempts to find out what happened to BT21 and endeavors to get back on his feet. Takuma had never been very close to his father, but by traveling back in time and in effect reliving the difficulties his father had contended with, he develops a deep admiration for him. He also learns of the unfulfilled love between his father and coworker Kyoko Takeuchi, who was raising a daughter on her own after escaping an abusive husband. Everything he learns about his father becomes like a tailwind pushing him on his way toward recovery, and toward getting back together with his wife, Ami.