本是岭南大学学生的王佳芝(汤唯 饰)因战争辗转到了香港读书,她在香港大学加入了爱国青年邝裕民(王力宏 饰)组织的话剧组,他们主演的爱国话剧更激起了他们的爱国情操。当邝裕民得知汪伪政府的特务头子易先生(梁朝伟 饰)正在香港的时候,他们便密谋要刺杀易先生。化名“麦太太”的王佳芝很快得到了易太太(陈冲 饰)的信任与喜爱,同时美丽的“麦太太”也吸引了易先生的眼球,正当事情进行得如火如荼之际,易先生突然要回到上海去。 此后王佳芝一直生活在上海,没想到重遇了邝裕民。当得知刺杀行动还没结束时,王佳芝再次成为了特务,再次以“麦太太”的身份出现在易先生的面前。 重逢后的二人关系进一步发展,此时的易先生因爱上了王佳芝而对她毫无忌讳,王佳芝的内心也变得起伏不定。刺杀行动进行正顺利,但当易先生送给王佳芝璀璨钻戒表达爱意时,王佳芝做出了惊人的决定……Frustrated in his attempts to assassinate Yee, who is an important official in Japanese-ruled Shanghai, Old Wu, who has lost his wife and two sons as well as two women who had attempted to seduce Yee, now recruits Kuang, Mai Tai Tai, and their troupe of drama students from Hong Kong University in yet another attempt to do away with Yee. Mai Tai Tai is chosen to befriend Yee, which she does by posing as the wife of Mak, befriending Yee's wife and her female friends, and then eventually befriending Yee himself. Even though both get together, they do end up going separate ways, only to meet again four years later. This time Mai is all set to entrap Yee at Chandni Chowk Jewellers which is owned by an East Indian man named Khalid Saiduddin. The question does remain: Will she and her troupe succeed?