On a cloudless night in Narnia, amid the shadows of a menacing castle, Lady Protectress Prunaprismia (Alicia Borrachero) welcomes the birth of her son. However, not far down the hall, General Glozelle (Pierfrancesco Favino) hastens to deliver alarming news to Prunaprismia's husband, Lord Protector Miraz (Sergio Castellito). Miraz, eager to eliminate any threats to his rule, orders Glozelle to eliminate the rightful heir to the throne, young Prince Caspian (Ben Barnes), who is the tenth in line from the original Caspian, "The Conqueror".
However, Caspian's mentor, Doctor Cornelius (Vincent Grass), is determined to protect him. He awakens Caspian and ushers him into a hidden armoire, which leads to a secret passage. Just as Caspian secures his escape, Glozelle and his men enter, unleashing a volley of crossbows into Caspian's empty bed, scattering feathers into the air. As Caspian escapes into the Shuddering Woods, he is pursued relentlessly. He collides with a tree and is soon confronted by two dwarfs, one red-headed and the other black-haired. In a moment of desperation, he blows a mysterious horn, seeking help.
This horn's call resonates across dimensions, reaching 1942 London, where the Pevensie siblings—Susan (Anna Popplewell), Lucy (Georgie Henley), Peter (William Moseley), and Edmund (Skandar Keynes)—find themselves drawn back to their beloved Narnia. Their return is not seamless; upon arrival, they discover ruins of Cair Paravel, the castle where they once ruled. Meanwhile, Miraz's unjust reign is reinforced by a council that accuses him of being untrustworthy, while secretly plotting the capture of the rightful king.
In Narnia, Caspian learns hints of his destiny as he allies with Nikabrik, a dwarf, and Trufflehunter, a wise badger. Meanwhile, Miraz's tyranny escalates, inciting Caspian to forge alliances among the Narnians. As tensions rise, the Pevensie siblings and Trumpkin, a red dwarf, unite to confront the impending war against Miraz's forces.
As battle ensues, the stakes are high for both the Telmarines and Narnians. Peter leads a daring raid that goes awry, causing anguish and loss among their ranks. As the tide of battle seems to favor Miraz, the dormant powers of Narnia awaken, led by the legendary lion Aslan (Liam Neeson). The very trees and rivers rise to aid in the battle, turning the tide against the oppressive forces.
In a dramatic twist, as Miraz attempts to retain control, his own allies turn against him. Caspian ultimately assumes his rightful place as king, bridging the gap between the Narnians and the Telmarines. In an emotional farewell, the Pevensies realize their time in Narnia has come to an end, and they step through a portal back to Earth, leaving behind a renewed world brimming with hope and unity.
As the dust settles, Caspian stands amid his newfound kingdom, proclaiming a future where Narnians and Telmarines can coexist, fully aware that the horn he blew will always be a symbol of their shared history and the adventures yet to come.
