Arthur (the voice of James McAvoy), one of Santa’s two sons, is a bumbler who is assigned to the comparative busywork of answering children’s letters, while Steve (Hugh Laurie), his brother, is groomed to replace the aging Big Guy. Steve has coordinated the high-tech production and delivery system that enables Santa to meet the gift needs of the entire world in a single night. (It features a supercharged, reindeerless sleigh.) It’s Christmas Eve, and Steve is expecting Santa (Jim Broadbent) to retire once the last present is delivered, turning the Santa job over to him.
When the frenetic evening is over, everyone involved in the North Pole effort gathers under a big sign that says — gotta love this — “Mission Accomplished.” But just like the earlier high-profile instance when that phrase was displayed, the mission is not complete: one toy has been overlooked. Can Arthur and gnarly old Grandsanta (Bill Nighy) deliver it the old-fashioned way, and thus save Christmas?
At this point the plot starts getting unnecessarily busy — blame the government, which becomes involved when a strange radar blip suddenly turns up on defense systems, throwing the entire world into a panic.