An extraordinary light incident ten years ago led to the mysterious disappearance of Zhang Peng's friend. Ten years later, a film crew director approached Zhang Peng with the idea of returning to Xiangshan, the site of the incident—a remote small town built during the Sino-Soviet confrontation in the 1960s, known as the "Third Front"—to shoot a film seeking the truth.

身患老年痴呆症的吴宗华向来与家人不和，尤其与儿子吴咏关系紧张。就在吴宗华走向生命终点之前，他执意要回青年时期曾经工作过的嘉陵县去探望身患重病的老战友。由于父亲生活无法自理，儿子吴咏不得不陪伴吴宗华踏上了这段旅途。经过一番波折，两人终于来到嘉陵县，却没想到揭开了父亲年轻时一个不为人知的秘密。这也解释了父亲为何多年来一直对家庭照顾不周的原因——而这也正是一家人之间多年来最大的芥蒂和心结。在陪伴父亲走完生命最后的旅程之后，吴咏终于找回了与父亲之间的亲情，父亲吴宗华也在安详中离开了人世。