广告人隆之介(竹野内豊饰)、英太郎(阿部寛饰)、阿巧(妻夫木聡饰)是三个狐朋狗友,英太郎和女朋友亚纪(石田ゆり子)相恋多年,但总不肯和她结婚。一次野外沙滩派对,隆之介认识了亚纪的妹妹千代(広末涼子饰)。朦胧月色映射中,两人为海滩的浪漫气氛迷惑,体内荷尔蒙作祟,突然产生了相爱的冲动…… 不料一晚欢爱过后,亿万分之一“中奖”的机会居然发生了!千代发现自己意外怀孕,毫无心理准备的两人只得决定“奉子成婚”,这时他们才发现对对方一无所知,包括性格、习惯、生活方式等等,所有的一切都要从头来过,两人一边学习做父母的知识,一边在两人的相处中不断认识对方并与其磨合……不仅如此,结婚还牵涉到双方的家庭,面对千代食古不化的老爸(千葉真一饰),两人遇到了空前巨大的阻力。Hirosue Ryoko stars as Chiyo, 20, a department store clerk, whose first encounter with Ryunosuke, 30, a carefree bachelor friend of her sister's, leads to a pregnancy. Although of different worlds, they fell in love but Chiyo's father doesn't want these youngsters to get married. After eight months of struggles and growing up, they finally accepted each other as partner.