The four Pevensie children - Peter, Susan, Edmund, and Lucy - are evacuated from London because of the air-raids during WWII. They are sent to a very old house to stay with Professor Kirke. One boring, rainy day the children play hide-and-seek. Lucy hides in a large wardrobe stored away in a bare spare room. Through this, she enters another world called Narnia.
She meets a faun, Mr. Tumnus, who takes her back to his house for tea. He tells her that Narnia is always winter and never Christmas because of the White Witch. Lucy wakes with a start after falling asleep at his house, and gets back to the real world through the wardrobe. She tells her brothers and sister what happened, and they don't believe her, especially since she's only been gone a few seconds.
Later one night, Edmund sneaks away to see the wardrobe on his own, and also gets into Narnia. He runs into the White Witch, who, acting sweetly, gives him magical refreshments and ploys him to bring his brother and sisters back to her castle to meet her. Lucy finds out that Edmund has been to Narina, but he lies and tells Susan and Peter that he's only playing along with Lucy. A few days later, the children are playing outside when they break a window and run inside the house to hide from the professor. They all go into the wardrobe together to hide, and they are all able to enter Narnia. They try to go to Mr. Tumnus' house, but he has been arrested by the White Witch, who is not the real ruler of Narnia.
The children meet up with two animals, Mr. and Mrs. Beaver. They try to help the children, but Edmund sneaks away to the castle of the White Witch to tell her that his brother and sisters are in Narnia. She finally shows him her cruelty by locking him in her prison. She gets her wolves to track down the children and the Beavers. Meanwhile, the Beavers, who know how awful the White Witch is, run to find a safe place for the remaining three children. On their way, they hear that "Aslan is on the move." Aslan is a lion who is the true ruler of Narnia. Everyone is happy to hear this, and, as if to confirm their hopes, they run into Father Christmas which means that Christmas is coming and the witch's power is weakening.
The Beavers and children travel on to find Aslan. When they find him, they tell him about Edmund. The White Witch brings Edmund to Aslan, but says that, since he is a traitor to his family, he belongs to her and she has the right to kill him. Aslan offers himself to be killed instead, and Edmund is returned to his brother and sisters. But Aslan comes back to life. After Aslan is alive again, there is a huge battle between Aslan's side and the witch's side. The witch's side is eventually conquered, and the children are crowned kings and queens of Narnia.
Many years later, when the children are grown into adults, they're on a hunt for a white stag. The stag leads them back to the place where they entered Narnia. They go back through the wardrobe, and they're back at Professor Kirke's house. And, as if our time has stood still, they're the same age they were when they entered Narnia at the beginning of the story.