Peter Highman, played by Robert Downey Jr.](/actor/robert-downey-jr), is a tightly wound architect eager to return home from Atlanta to Los Angeles as he anticipates the birth of his first child with his wife, Sarah (portrayed by [Michelle Monaghan). Fearful of missing the moment, Peter is on edge about getting there in time. Amidst their typical pre-baby name debates—where Peter insists their baby will be a boy—unexpected chaos ensues.
Trouble arises when Peter discovers that a peculiar passenger named Ethan Tremblay, played by Zach Galifianakis, is seated directly behind him on the plane after a series of misfortunes that involve an altercation with Peter’s limousine. This encounter leads to a cascade of mishaps, including Peter accidentally picking up one of Ethan's bags containing a marijuana pipe, discovered by airport security!
The airplane journey spirals out of control as Ethan's antics — from his awkward personal space issues to unwittingly invoking the words "terrorist" and "bomb" — culminate in Peter being shot with a rubber bullet by a Federal Air Marshal, resulting in both men being escorted off the flight before it can even take off. Soon, Peter learns he’s now on the No-Fly List and realizes he possesses nothing but a plane ticket, leaving him without ID, cash, or options for transport to California.
With no way to rent a car, Peter reluctantly teams up with Ethan, whose goofy charm and ambition to be an actor serve as both a frustration and an unexpected source of camaraderie. As they hit the road, Ethan's plan to stop at the Grand Canyon to scatter his father's ashes — contained, much to Peter's confusion, in a coffee can — presents further strife. Stopping in Birmingham, Alabama to procure more marijuana under the guise of "medical purposes," the duo discovers they have a mere $60 between them after Ethan squanders funds on drugs. Attempts to wire money to Peter through Western Union result in frustrating farce, particularly when the employee refuses to accept Ethan’s headshot as identification, leading to a confrontation that ends with Peter at odds with a wheelchair-bound man.
As the journey progresses, they encounter a series of misadventures, attempting to escape various complications, including a car crash caused by Ethan dozing off at the wheel, and even a brief stint in a hospital following Peter's injuries. Despite Peter's initial desire to ditch Ethan, their bond deepens through laughter and mishap, culminating in heartfelt moments where they support each other more than they initially thought possible.
In a hilariously disastrous border crossing into Mexico, Peter finds himself arrested for the marijuana possession — all while Ethan inadvertently facilitates his escape amid wild chaos, driving a patrol truck through the fray. They manage to arrive at the Grand Canyon, where Ethan finds closure with his father's ashes amidst Peter's conflicted emotions, revealing the delicate threads of their friendship.
Their adventure reaches a peak as Peter's phone rings with news of Sarah going into labor; the stakes have never been higher. However, mishaps ensue, including an accidental gunshot wound inflicted by Ethan in a moment of panic! Despite the odds, they race to the hospital, fraught with tension that tests their newfound friendship.
Ultimately, as they reach the hospital and Peter bravely encounters his wife while teetering on the brink of unconsciousness, it’s a gripping moment that shows the unmistakable bonds formed through adversity. As their baby girl arrives safe and sound, the two men part ways with a promise of ongoing friendship. In a charming twist, Ethan makes an appearance on "Two and a Half Men," with Peter and Sarah sharing a cozy moment at home, hinting that their wild adventure has shaped a humorous, heartfelt connection that bridges their vastly different worlds.
