An armored truck of the U.S. Treasury is robbed. The thieves ignore the millions of dollars in cash, taking only the engraving plates being transported in the truck, which are then delivered to an oddly-dressed man waiting on a nearby rooftop. The daughter of mild-mannered Manhattan dentist Sheldon "Shelly" Kornpett and the son of businessman Vince Ricardo are engaged to be married. At an introductory dinner Shelly (Alan Arkin) meets his new in-law, Vince (Peter Falk), the man from the rooftop. Sheldon finds Vince suspicious for several reasons, including, during the dinner, when Vince tells a crazy story of a nine-month "consulting" trip to 1954 Guatemala. Vince's son and wife seem oblivious and used to his antics. At one point in the dinner Vince excuses himself to make a phone call and, when he is told something that worries him, he hides something in the basement of the Kornpett home. Later that night Shelly urges his daughter not to marry into the Ricardo clan, but he is talked into giving the marriage a chance.