Everyone knows that, each Christmas, Santa Claus delivers presents to every last child on Earth. What everyone doesn't know is that Santa accomplishes the feat with a very high-tech operation beneath the North Pole. But when the unthinkable happens, and Santa misses one child out of hundreds of millions, someone has to save the day. It's up to Arthur (James McAvoy), Santa's youngest son, to deliver a present to the forgotten tyke before Christmas morning dawns.