凯西（詹妮弗·安妮斯顿 Jennifer Aniston 饰）是个年近四十的单身女人，她有工作，有朋友，尽情享受单身生活，也萌生了生一个小孩独自抚养的想法。联系相关机构后，凯西找到和合适捐精人——完美先生罗纳德（杰夫·高布伦 Jeff Goldblum 饰），不想在好友为她举办的“受孕派对”上，她最好的朋友沃利（杰森·贝特曼 Jason Bateman 饰）在卫生间气恼地换掉了罗纳德的精液。原来沃利一直爱着凯西，只是二人做好友太久了，已经失去了走在一起的最佳时机，就这样眼睁睁看着凯西离开自己。一别七年，凯西再次回来纽约居住时，带回了7岁的早熟小孩塞巴斯蒂安，迎接他们归来的沃利轻易发现塞巴斯蒂安和自己的相似，他想适时告诉凯西真相顺便表白，不想罗纳德也再度出现在凯西生活里……Kassie (Jennifer Aniston) and Wally (Jason Bateman) are best friends. Being unlucky in love, Kassie has decided to have a child using artificial insemination. Wally doesn't like this idea, but he isn't capable of admitting to himself, let alone to Kassie, that he's in love with her. At Kassie's artificial insemination party, Wally gets very drunk and spies the sperm donor's sample in the bathroom. Wally was way too drunk to know what he did that night, and Kassie has moved away because she doesn't feel that New York City is a place to raise a child. Now 7 years later, Kassie has moved back with her son Sebastian. While she is looking to get Roland (the sperm donor) more involved in their lives, Wally can't help but notice the many striking similarities that he and Sebastian share.