It's Christmas Eve and Hero Boy (voice of DARYL SABARA) can't get to sleep. At the age when kids start to question the existence of Santa, he's uncertain but still hopes that the gift-giver is real. Thus, with every noise in the house late at night, he thinks it might be him, but is disappointed when it isn't.
The next noise he hears, however, is unmistakable. It's a huge locomotive and its accompanying train that has stopped right in front of his house. And its Conductor (voice of TOM HANKS) wants him to come along for a ride on the Polar Express that's headed for the North Pole. Hero Boy is initially reluctant, but when the train starts to pull away, he races for and boards the Express.
There, he meets other kids, such as the confident Hero Girl (voice of NONA GAYE) and the nerdy Know-It-All (voice of EDDIE DEEZEN), who are there for the same reason. Along the way, they pick up Billy (voice of JIMMY BENNETT), a lonely kid from the wrong side of the tracks who claims that Christmas has long since passed him by.
Hero Boy and the other kids then have encounters with various individuals onboard -- such as a mysterious Hobo (voice of TOM HANKS) who rides atop the moving train, and train workers Smokey and Steamer (voice of ANDRE SOGLIUZZO) -- as well as several perilous adventures. As the train makes its way north, the kids can't begin to imagine what they'll see when they eventually arrive and then set out to meet Santa Claus (voice of TOM HANKS).