As a child, Prince Caspian was told stories of old Narnia by the nanny. When his uncle, King Miraz, found out about this, he sent her away. A tutor, Doctor Cornelius, was brought in to teach Caspian properly. When the tutor arrives, he starts with history, telling the boy about his name sake from King Caspian I to King Caspian IX (the last of which was his father). Some years later, when Caspian is older, King Miraz has a son. Cornelius warns Caspian that he must flee because he should be the true king of Narnia, but Miraz won't let that happen know that he's had a son. He also informs him that Miraz killed his father. Caspian flees on his horse taking the horn of Queen Susan. The horse eventually tosses Caspian and he is knocked unconscious.
Meanwhile, back in London, the Pevensie children (Peter, Susan, Edmund, and Lucy) are preparing to return to school. Lucy is the most upset about it as it is her first year. Edmund tries to cheer her up while Susan can't seem to understand her feelings at all. It has been a year since they left Narnia and Lucy misses it terribly.
Caspian wakes up to find that his head has been bandaged by two dwarves, Nikabrik and Trumpkin and a badger, Trufflehunter. They are debating over what to do with him when he tells them that he believes in Old Narnia. They accept him as the true king of Narnia and start to gather all of the talking animals, dwarves, and other creatures they can find to fight the forces of Miraz's army. Doctor Cornelius arrives and warns them that Miraz is already on the way. They decide to get better ground at Aslan's How, which is close to the ruins of Cair Paravel (whose forests are supposed to be haunted). While there, Caspian decides that it is time to blow on the horn and does so.
Peter, Susan, Edmund, and Lucy are transported back to Cair Paravel. At first, they don't recognize the place because it has been hundreds of years since their rule. But they find the gifts that Father Christmas gave them all that time ago. They see that a dwarf has been captured and that two men
are going to drown him. Susan fires an arrow, scaring the men. They save the dwarf and learn that he is Trumpkin, sent by King Caspian. They decide to set off to join the new future king of Narnia.
On their journey, Lucy sees Aslan and tells everyone which way to go. However, none of them believe her and they keep going the way that they think they should. In the middle of the night, when they can't sleep, Aslan appears to Lucy and tells her to wake the other and follow him. Eventually, she is able to convince all of them to do so, even though it is some time before Aslan is revealed to the others. The Lion sends Peter, Edmund, and Trumpkin ahead to Caspian. Susan and Lucy stay with Aslan to wake up the trees for the upcoming battle.
Peter, Edmund, and Trumpkin arrive to find that Nikabrik is trying to call upon the White Witch for help. He has already brought a Hag and a Werewolf into their hideout. The argument escalates into a fight and Nikabrik and the Hag are killed. The werewolf bites Caspian before he gets away.
Peter sends a challenge to Miraz. Miraz doesn't plan to accept, but his greedy lords, Glozelle and Sopespian, trick him into accepting the challenge, hoping that they can claim the power when he is slain by the High King Peter. The fight ensues, and Miraz uses a dirty trick to make it look like Peter stabbed him in the back. Miraz's army charges and the battle has begun. Aslan shows up with the girls and the trees. Narnia wins and Aslan give them a choice of returning to their island in the real world or staying in Narnia under Caspian. Aslan creates a door and a man volunteers to go through. Before the four children return to their own world, leading the rest of the army that wants to go, Aslan reveals that this was Peter and Susan's last time in Narnia. They are returned to the train station they were waiting at before their adventure started and Susan and Lucy's train arrives to take them to school.
The Chronicles of Narnia:
The Lion, The Witch, and the Wardrobe
The Voyage of the Dawn Treader
The Silver Chair
The Horse and His Boy
The Magician's Nephew
The Last Battle