Bob and Greta De Jaegher are happily married for 40 years. They can look back on a rich and fulfilled life. Their 2 sons Steve and Carl have a successful life as well. Steve is a talented and recognized film-director and Carl is a promising cook. Steve's wife Billie wrote a bestseller about happiness and wants to start a family with her husband. Brother-in-law Rik, who works at the zoo, tries to pick up his life with his kids, after his wife died two years ago. To mark their 40th wedding anniversary, Bob and Greta organize a family weekend. They want to announce something very important. Their new plans are a sure hit for the family De Jaegher, but that's not the only thing - Wat had to be a cheerful gathering of the family, turns out to be something nobody expected.
爱丽丝（邦尼·亨特 Bonnie Hunt 饰）和乔治（查尔斯·格罗丁 Charles Grodin 饰）带着三个孩子瑞思（尼科洛·汤姆 Nicholle Tom 饰），泰德（Christopher Castile 饰）与艾米丽（Sarah Rose Karr 饰）住在城郊的大房子里，生活过得平静而又幸福，直到一天，一只可怜又可爱的流浪狗出现在了纽顿家门口。在三个孩子的苦苦恳求下，小狗成为了纽顿家新的一员，取名贝多芬。
时间流逝，长大的不仅仅是纽顿家的三个孩子，还有贝多芬，在短短几个月的时间里，原本娇小可爱的贝多芬已然成为了一只庞然大物，在不断制造麻烦的同时，贝多芬也为纽顿一家带来了深深的快乐。贝多芬的存在吸引了兽医瓦尼克（迪恩·琼斯 Dean Jones 饰）的注意，邪恶的医生开始想尽千方百计，企图将贝多芬据为己有。
