故事发生在1940年代的香港，妙龄少女方兰（周迅 饰）和母亲（叶德娴 饰）一起过着相依为命的生活，两人将家中的二楼租住给了作家茅盾（郭涛 饰）和其太太孔德沚（蒋雯丽 饰）。方兰十分热爱茅盾的文字，在其中感受到了火热的革命热情和澎湃的民族气节，然而对于身边动荡的时局和紧张的政治氛围，方兰却知之甚少。 刘锦进（彭于晏 饰）是拥有着矫健身手的进步青年，受组织委托，他负责护送滞留在香港的一批重要文人返回大陆，茅盾一家人便在名单之列。在误打误撞之中，方兰被卷入了这一危险的行动之中，并在刘锦进的建议和鼓励之下，加入了革命队伍之中去，母女两人因此被卷入了历史的滚滚洪流之中。1941. Hong Kong is under Japanese occupation. The anti-Japanese Dongjiang guerilla unit is tasked with rescuing cultural figures and extracting them from the besieged city. Primary school teacher, Fang Lan and her mother are trying to live out this difficult period in a small run-down flat in Wanchai. After the schools are shut down, Lan unwittingly finds herself involved in the guerillas' mission to save novelist Mao Dun. In the process, she meets Blackie Lau, the intrepid sharpshooter captain of the guerillas' Urban and Firearms unit. Taking notice of Lan's calm, smart nature, Blackie recruits her to join the guerillas. Worried for her daughter's safety, Lan's mother volunteers to take Lan's place as a courier, only to be arrested on the job. To save her mother, Lan is forced to turn to Wing, who now works for the Japanese.