Four children named Peter, Susan, Edmund, and Lucy go to the country to live in the large, mysterious house of an old Professor during the London air raids. One rainy day, the children take the opportunity to explore the house, peeking into spare bedrooms and old passageways, until Lucy, the youngest, pauses to look into a large wardrobe sitting in an empty room. She crawls past the long fur coats and finds herself standing in the middle of a forest. It is night, and snow is falling, though in London it is summer. She walks toward an iron lamp-post and, thinking it is strange to come to a lamp-post in the middle of a wood, is met by a very surprised faun.
This faun, confirming that Lucy is a human girl, or a "Daughter of Eve", invites her for tea, snacks, stories, and music in his cozy little cave. She trusts the faun and follows him, staying with him for what seems like many hours. Suddenly, she exclaims that she must be getting back, and the faun, Mr. Tumnus, begins to cry. He explains that he is in the service of the evil White Witch, who has cast a spell over Narnia so that it is always winter, yet never Christmas. Narnia is the name of the world into which Lucy has stumbled, a world that stretches from the lamp-post to the eastern sea. Mr. Tumnus, however, decides to save Lucy, and leads her quietly back to the lamp-post. She flees through the wardrobe door, and, tumbling out, cries that she is alright. For her brothers and sisters, however, no time has passed since they had last seen her. Lucy excitedly shares with them the news about Narnia, but when they check inside the wardrobe, they find that it is quite ordinary.
The next rainy day, while the children play hide-and-seek, Lucy crawls back into the wardrobe. Edmund, seeing her disappear, follows her and finds himself standing in the middle of a wood on a winter day. He reaches the lamp-post, calling out to Lucy, when a sledge pulled by reindeer comes to a halt. A lady in white fur with a gold wand and crown announces that she is Queen of Narnia and asks Edmund who he is. When she realizes that he is a human boy, or a "Son of Adam", she invites him to sit with her in her sledge, and conjures for him a warm drink and, at his request, a box of Turkish Delights. As Edmund eats the Turkish Delights, she tells him to return with his brother and sisters to her house, which she points out between the two hills in the distance. She leaves him at the lamp-post, still craving more Turkish Delights. Lucy finds him and is excited that he has made it through; together, they tumble out of the wardrobe, and Edmund tells Susan and Peter that they had been pretending to be in Narnia. Lucy runs away and cries, and Susan and Peter, worried that Lucy has gone mad, go to talk to the Professor. The Professor, to their surprise, asks them why they do not believe Lucy's story, since logic suggests that she is telling the truth.
One day, the housekeeper gives the children strict instructions to keep out of the way while she leads a tour group through the house, which is quite famous. As the children are playing, they suddenly realize that they are about to run right into the group. All four rush into the empty room, and into the wardrobe. Within moments, they find themselves standing in a wood. Peter apologizes to Lucy for not believing her, and Edmund gives away the fact that he had been lying about previously having been in Narnia, angering Peter. Lucy leads the group to Mr. Tumnus's house, but when they arrive at his door they find that he has been arrested. A red robin leads them to Mr. Beaver, who takes them home, where Mrs. Beaver has prepared dinner. Mr. Beaver explains that Mr. Tumnus has been arrested, and has probably been turned into stone at the Witch's house. In the meantime, he has received word that Aslan is near and that they are all to meet him the next day at the Stone Table. After some time, Lucy realizes that Edmund has gone, and Mr. Beaver expresses his belief that he has gone to the White Witch. They hurriedly prepare for the journey to the Stone Table and spend the night in an old hiding-place, waking in the morning to the sound of bells. Father Christmas has come, a sign that the Witch's spell is beginning to weaken. He presents gifts to each of them, as well as a wonderful tray of tea.
Meanwhile, Edmund makes his way through the cold night to the Witch's house and discovers a courtyard of stone statues. He is let in, and tells the Witch that his brother and sisters are at the Beavers' house, and that Aslan is coming. The Witch is astonished and sends her wolves after the Beavers and the children, ordering her sledge to be prepared. Edmund realizes that is to be given no more Turkish Delight, and begins to feel that he has made a big mistake. He is ordered into the sledge next to the Witch, and after traveling through the cold, they come into view of a small party celebrating Christmas morning in the wood. The Witch turns them into stone; when Edmund tries to stop her, she slaps him. The coming spring has made it impossible for the sledge to continue any further, so they begin walking, Edmund's hands tied tightly behind his back.
When the Beavers and Peter, Susan, and Lucy arrive at the Eastern Sea, where they find the Stone Table and Aslan, the great lion, Aslan asks where the fourth has gone, and Mr. Beaver explains that Edmund has betrayed them to the Witch. Peter is then shown the castle of Cair Paravel, where there are four thrones waiting to be filled. Suddenly, they hear cries. The Witch's wolves have arrived, and Peter, in a show of courage, kills the leader by striking him in the heart. In appreciation for this act of bravery, Aslan makes Peter a Knight.
Edmund, meanwhile, is exhausted from the walking. He and the Witch come to a halt in a valley, where she ties him to a tree and prepares to kill him. At that moment, there is a commotion, and Edmund faints. The Witch and her dwarf escape, but Edmund is saved by Aslan. In the morning, he walks with Aslan, and they share a private conversation. When they return, Edmund tells his brother and sisters that he is sorry, and they all forgive him. The Witch then seeks an audience with Aslan. There is discussion about a deep magic that requires traitors such as Edmund to be handed over to the Witch. Aslan, however, takes her aside and reaches an agreement, one that no one dares ask about. The Witch goes, and the rest set up camp for the night.
During the night, Susan and Lucy have trouble falling asleep, feeling that something horrible is about to happen. They notice Aslan walking into the wood, and decide to follow him. He realizes that they are following him, and they walk together to the Stone Table, where Aslan tells them that they must hide. They watch as he approaches the evil group, led by the Witch. He is tied down, and the Witch kills him with a knife. In the silence that follows, the two girls approach the dead body and begin to weep. As the sun rises, however, they hear a loud crash: the Stone Table has been broken. They find Aslan alive, and very real. He explains that there is another magic, deeper than the one the Witch knows, a magic from before the dawn of time. It allows the one who dies in the place of a traitor to come back to life. The two girls climb onto him, and Aslan leaps through the country to the Witch's house, where he jumps over the wall into the courtyard. Once there, he brings all of the stone statues back to life - including Mr. Tumnus.
Having organized themselves to battle the White Witch, the group quickly proceeds to a narrow valley, where Peter, Edmund, and Aslan's army are fighting the Witch and her followers. Aslan pounces on the Witch and kills her, winning the battle. Edmund is injured, and Peter explains to the others that Edmund was the one to destroy the Witch's wand. Lucy uses her Christmas present, a little bottle full of the juice of fire-flowers from the sun, to restore him. Aslan instructs her to tend to the others, as well. Edmund improves, and is better than ever before. Aslan makes him a Knight.
There is a celebration at Cair Paravel, and the prophecy comes true: the four thrones are filled by two Sons of Adam and two Daughters of Eve, and Peter, Susan, Edmund and Lucy each grow in renown. They rule Narnia fairly for many years, until one day, as they hunt for the White Stag in the Western Wood, they come upon a lamp-post. It strikes them all oddly, like something from a dream. They move beyond it, and suddenly the trees become coats, and they tumble out of the wardrobe in their old clothes. The housekeeper and the tour group are just passing by in the hall.
The children tell the Professor the story in order to explain why four of the fur coats from the wardrobe are missing. He believes their story entirely, and assures them that one day they will see Narnia again. He repeats what Aslan said to them as they had assumed their thrones: they will always be kings and queens of Narnia.