影片讲述了因不明感染事件而被封锁的建筑内，孤立无援的幸存者们对抗以无法预测形态进化的感染者的故事。
故事发生在土地革命时期的江西某地。忠犬赛虎为旺崽（李浩 饰）最爱，地主家少爷赵玉堂（赵一工 饰）垂涎这只颇通人性的好狗，几次欲买，均遭旺崽拒绝。一次，赛虎误入赵府，被赵玉堂捉到锁住，旺崽设计让赵府丫环小琴（戴菁 饰）把狗救出，为此小琴被打得浑身是伤。深夜，旺崽与父亲（何宁康 饰）在山崖下救下了从赵府逃出来的小琴，藏在山下草棚中。赵府派狗腿子到旺崽家翻箱倒柜，也没发现小琴的踪迹。旺崽爹闻听山外方志敏领导穷人闹革命，有意投奔。但又不知他们具体在何处，便安顿好孩子们，只身外出打探，不料行迹被赵府的人发现，被捕关进土牢。旺崽闻讯，带赛虎下山救父......
The crooks in London know how it works. No one carries guns and no one resists the police. Then a new gang appears that go one better. They dress as police and steal from the crooks. This upset's the natural order of the police/criminal relationship and the police and the crooks join forces to catch the IPOs (Impersonating Police Officers), including an armored car robbery in which the police must help the gangs to set a trap.
