因为母亲外出打工，旺旺（林浩 饰）自幼就与爷爷（陶泽如 饰）在断桥镇上相依为命。每当油菜花开的时候，旺爷都要带着旺旺接妈妈，但始终没有接到。这一年，一个临产的女人（余男 饰）意想不到地上了旺爷的船。看着女人给婴儿哺乳，从来没吃过母乳的旺旺萌发出对母爱深深的渴望，他狠狠咬了女人的乳房，而这在民风淳朴的小镇上引起了轩然大波…… 三个处于特殊生理周期的人，因此演绎出一段旷世真情。 电影改编自作家毕飞宇的同名短篇小说。

On an old barge moored close to a small village inhabited by old people and children, live young Wang Wang and his grandfather. The latter is immensely fond of the local doctor, Ms. Bei, who keeps prompting him to buy her a ring as proof of his good intentions. Wang Wang attends the local school, but, in the absence of maternal authority, with great reluctance. Then, one night, a young pregnant woman is discovered hiding on the boat, ready to give birth. With the arrival of her little baby girl, the young mother, already used to her river accommodations, opts to stay with them. Life on the barge is no longer the same. Wang Wang feels the stirring of adolescence and an Oedipal attraction to the young woman; the grandfather is diagnosed with dementia and and is warned that its first signs could soon manifest themselves; and the new young mother keeps a bag whose contents will later reveal a dark secret. Three people at a crossroads in their lives.