Four guys - divorced playboy Laird, meek homemaker Aubrey, conservative Gracen and eager newlywed Dougie - open up to one another about hopes, dreams and crises during their daily commute to and from work.
We are introduced to Aubrey, Gracen, Laird, and Dougie, who is joining the carpool for the first day, as they commiserate about life and sing old songs on their way to work. Gracen is discouraged to learn that his wife and son make more money than he does.
Laird borrows Gracen's wedding ring because he thinks it will make him more desirable to a woman. Marmaduke thinks that Laird may be his real father and Aubrey is seen sneaking into a motel by Dougie, who thinks the worst of it.
Laird is frustrated to learn that not only does he have a low sperm count, but that Gracen has a much higher count. Dougie has to perform some manual labor in order to help Aubrey get a hot spot at a top notch pre-school.
The men think they accidently set the car of a rival carpoolers group on fire as a result of a prank, but swear to keep it between themselves. Marmaduke's ATM machine with an $8 service charge is vandalized.
Laird claims to being sexual harrassed at work by a female co-worker in order to spend more time with the sexual harrassment seminar leader that he has the hots for. Leila asks Marmaduke to help her in creating a unique sign for her real estate flipping business.
Dougie and Cindy have their first fight when she doesn't trust anyone to babysit their child after Dougie wins tickets to a Spin Doctors concert. Leila doesn't notice a typo in her flyers that she is handing out that makes it appear she is a hooker. Laird opens his home to a neighborhood stray, only to discover it's a wild coyote.
As a last resort when there are no remaining open spots in the special lot for carpoolers, Laird decides to park in a spot reserved for the handicap. In order to not get in trouble, he lets Gracen to act like he has a bad limp. The parking attendant figures it out and bans them from the lot and also sends some bad karma their way.
Can the carpool group be friends outside of the car? That is the question Aubrey ponders when he invited the group to his daughter's piano recital. Marmaduke helps Gracen train for the annual charity run and for the chance to finally beat Leila.