抗日战争年代,一群亡命之徒集结在北方平原。他们在首领方有望(黄晓明 饰)带领下,建立了一个地下王国,平日打劫为生。一日他们绑架了一个正去迎亲的新郎官高栋梁(张译 饰),出乎意料的是,高栋梁是个硬汉子,很快凭自己的血性和智慧征服了整个匪帮,成为“二当家”,他和首领之妹“小姑奶奶”方梓珍(张歆艺 饰)产生感情,又说服方有望前去对抗日本侵略者,从绑架来前线视察的“天皇弟弟”开始。经过一番精心策划,这群案底累累的恶棍担起“匹夫之责”,凭借手中武器和血肉之躯,潜入日本人营地,试图搞出一番大作为……The movie is set during the Japanese invasion of China. The story is told from the perspective of Gao - a soldier seeking revenge from the Japanese. He is trying to assassinate the visiting Japanese commander. In the process of plotting such scheme, he had a chance encounter with a local Mafia, lead by its charismatic leader Fang. Fang has a band of followers, including his own sister. Fang have rescued many of the members of the band and formed a life-long friendship with them. When Gao realizes that he could use the help of Fang's band, he sets up a scheme to be captured by Fang on purpose. When Fang finds out - he is extremely angry and almost kills Gao. Gao is saved by Fang's sister after she see how he fared during an interrogation. Gao later redeems himself by saving Fang and all of his band when a bank robbery goes wrong. From there on, Gao partners with Fang to take down the Japanese chief in command. Pi Fu in Chinese means a commoner, and this is a movie about friendship, loyalty and brotherhood.