Peter Highman (Robert Downey, Jr.), a successful architect, is due to fly home from Atlanta to Los Angeles to be with his wife Sarah (Michelle Monaghan), who is about to give birth. On the way to the airport, he has a chance encounter with Ethan Tremblay (Zach Galifianakis), who is going to LA to be an actor and is planning to scatter his recently deceased father's ashes at the Grand Canyon. When Ethan misuses the words "terrorist" and "bomb" while talking to Peter, they are both escorted off the plane. This is only the first of a series of misadventures caused by the drastically dysfunctional Ethan. Peter, now on the No-Fly List and missing his wallet, agrees to drive with Ethan to Los Angeles. Ethan stops to buy marijuana, and Peter discovers that they are nearly out of money. Since Peter has no I.D., he gets his wife to wire the money to Ethan, but discovers Ethan had the money wired to his stage name instead of his legal name. When the Western Union employee (Danny McBride) refuses to accept Ethan's "Stage name I.D." it leads to a violent altercation.