尽管父亲是著名的婚外情调查专家,尽管见识过了无数的忠贞感情最终化为泡影,艾莲(奥黛丽·赫本 Audrey Hepburn 饰)却依旧对爱情有着无限的期望和憧憬,她甚至觉得,只有那些明知不道德却还要迎难而上的恋情才能算的上是真爱。一次偶然中,艾莲结识了父亲的调查对象法兰肯(加里·库柏 Gary Cooper 饰)——一个在情场上如鱼得水的风流浪子。 艾莲捏造了虚假的身份,开始在法兰肯面前扮演起了神秘女郎的角色,没想到,自己的纯情和真挚竟然猎得了这位浪子的真心。法兰肯拜托私家侦探调查艾莲的踪迹,没想到这位侦探正是艾莲的父亲。迫于父亲的压力,本来心心相印的两人只得分手,一对天设地造的情侣眼看这就要擦身而过。In Paris, detective Claude Chavasse is hired to follow a wife suspected of infidelity with the notorious American libertine Frank Flannagan. When the husband learns that his suspicions are accurate, he tells Claude of his plan to kill Flannagan. Claude's daughter Ariane overhears the threat and warns Frank of the coming trouble. She then plays the part of a worldly socialite with a list of conquests as long as Flannagan's. The bemused ladies' man returns to America the next day and Ariane, completely in love, follows his romantic escapades in the news. She sees him again in Paris the following year, and resumes her worldly guise, telling tales of former lovers when they meet at his hotel in the afternoon. Frank, amazed by the mystery girl and surprised to find himself jealous of her past, hires Claude to uncover more information about her. When the detective realizes what has happened, he asks Frank not to break his daughter's heart.