Adam's wedding has a rustic theme. It's in the country and there are cows. But he is stood up; the maid of honor hands him a note from his fiancee, which reads simply "I'm sorry." As the wedding guests head out of the church, taking their gifts, cows are seen overrunning the banquet food. Segue three years ahead to the main story--Adam has found a new girl, Holly, but every friend's wedding they attend has Adam puking his guts out. He and Holly are serious enough, however, for Holly to consider turning down a twice-her-current-salary job offer, even though Adam still has a problem with weddings. Adam goes so far as to buy a ring for Holly, but returns it when he can't bring himself to propose.
Unlike Holly, Adam's job is on the line unless he can sell a cow comic strip, "Kreature Korner," to newspapers in his territory. He's not made one sale until he meets up with Jimmy, an editor he once encouraged. Out of the blue, Jimmy asks Adam to be best man at his wedding, which is about to take place in a week. Knowing his problem with weddings, how can Adam say yes? But Jimmy makes a deal to buy the comic strip if Adam goes along, so Adam agrees. Adam and Holly head out to Grass Creek and learn why Jimmy has asked an almost total stranger to be his best man. Jimmy has grown up in an INCREDIBLY tiny town and he didn't want any of his fiancee DeeDee's brothers to be best man as they would get to run the whole show. Unfortunately, Adam has to deal with the whoppers Jimmy has made up about him, such as being a Heisman trophy winner who now has a brain shunt and a glass eye. Meanwhile, the entire wedding party has to deal with the problem of Lester, DeeDee's ex-boyfriend who can't stop showing up to profess his love for her.
When DeeDee's brothers kidnap Jimmy and Adam as a prank on the night before the wedding and leave them miles out of town in their underwear, Jimmy and Adam's walk back involves a conversation where Adam inadvertently describes getting married as putting the woman in charge of his marriage. It rattles Jimmy such that right after the wedding ceremony gets underway, he bolts out the door and Adam has to go after him. Holly chases after the two only to hear a recap of what Adam has said. Fed up, she tells Adam she can't wait any longer for him to deal with his problem, and leaves. Then Lester appears on the scene with a shotgun to stop the wedding. Since he can relate to what Lester's going through, Adam is able to talk to Lester into releasing both his gun and his pain. As he accomplishes this and gets Jimmy back to the ceremony, Adam realizes he has cured himself and goes after Holly.