It's WWII era England and the Pevensie kids -- teenagers Peter (WILLIAM MOSELEY) and Susan (ANNA POPPLEWELL) and their younger siblings Edmund (SKANDAR KEYNES) and Lucy (GEORGIE HENLEY) -- not only have to deal with their father being off in the war, but also constant bombing raids by the Nazis. When the latest is too close for comfort, their mother puts them on a train where they head off into the countryside to stay at an enormous manner owned by Professor Kirke (JIM BROADBENT).
With his steely housekeeper informing the kids not to disturb him, they try to find ways to amuse themselves, and the older kids eventually agree to play hide and seek with Lucy. During the game, Lucy discovers an otherwise empty room containing only a covered wardrobe. Deciding it would make a good hiding place, she scurries inside, only to discover that it's much bigger than it seems and eventually leads to a wintry world that she soon will learn is called Narnia.
There, she meets the Faun Mr. Tumnus (JAMES MCAVOY), but doesn't realize his seemingly kind ways are really a ploy to kidnap her for Jadis, the evil White Witch (TILDA SWINTON) who's ordered that any such humans be rounded up and delivered to her. Tumnus is conflicted by what's the proper thing to do and thus helps her escape back to her world.
Her siblings don't believe her story, even after Edmund follows her into Narnia and encounters Jadis, before returning to the manor. Yet, after accidentally breaking something, all four try to elude the housekeeper and end up hiding in the wardrobe. It's then that Peter and Susan realize Lucy was telling the truth. They also discover that Tumnus has now been deemed a traitor and the kids then find a new guide in the form of Mr. Beaver (voice of RAY WINSTONE).
He takes them back to his home where he and Mrs. Beaver (voice of DAWN FRENCH) inform them that the White Witch has subjected Narnia to a century of winter, but without Christmas. They also state that prophecy foresaw the two sons of Adam and the two daughters of Eve arriving in Narnia to free the inhabitants from the White Witch's rule.
The Pevensie kids don't believe they're the ones, yet with the aid of the Beavers and a slinky Fox (voice of RUPERT EVERETT), they're soon on their way to meet the mighty lion Aslan (voice of LIAM NEESON) who's gathering an army of mythological creatures to battle the White Witch and her forces.