Peter Highman (Robert Downey Jr.) will be a dad for the first time when his wife gives birth in five days. He intends to catch a flight home from Atlanta so he can be there for the delivery, but a chance encounter with aspiring actor Ethan Tremblay (Zach Galifianakis) throws a monkey wrench into his plans. Desperate to reach his wife before their baby is born, Peter's sanity is tested when he must take a road trip cross-country with dog-toting Ethan.