The Telmarines long ago invaded Narnia from the nearby country of Telmar. They drove out the Old Narnians and slaughtered nearly all o them. They went into hiding in the woods, which the Telmarines began to fear.
Many years after the original invasion and Prince Caspian is now hear to the throne. His evil uncle killed his father and all the men who were loyal to him. Now that he has a son of his own, he plans to kill Caspian. Caspian's tutor, who is half dwarf, warns him and he flees into the woods with a gift: Queen Susan's magical horn.
The Narnians are suspicious of Caspian, at first, when he flees into their woods, but they learn to love and trust him as on of their own. Caspian loved the tales of Old Narnia that his tutor used to tell him, he was not like the other Telmarines. He gathers an army of all the Old Narnians who are left and march to Aslan's How, a very sturdy stronghold. When Miraz, Caspian's uncle, discovers he is gone, he sends scouts out to look for him and then sends his massive army. Caspian is unsure of what to do, but he knows they can't fight Miraz's army alone, so he blows the horn. This causes Peter, Susan, Edmund, and Lucy, the kings and queens of Old Narnia, to come to Narnia. In Narnian time, it has been thousands of years since they were last here, and many people doubted that they even existed. They travel to Aslan's How to meet Caspian and his army. Thanks to Lucy, they have also found Aslan, who plans to help them. Lucy and Susan stay with him in the woods to help him wake up and gather the trees together. Peter and Edmund meet with Caspian and decide their plan of action. The next day, Edmund is sent to Miraz with a challenge from Peter: single combat on the field of battle. The reward is total surrender.
When Peter fights Miraz, he wins, sort of. Miraz was actually killed by his own men, who were also power hungry. They blamed Peter for an unfair fight and call in the waiting army. The Narnians fight heroically, but are soon being surrounded until, out of nowhere, the trees start to come oft of the woods. They are led by Aslan and the attack the terror stricken Telmarines, who flee for their lives. The Narnians chase what is left of their army through the woods to the Fords of Beruna, where they are trapped because the bridge has been destroyed by the river-god.
After this, Caspian is crowned King of Narnia, and the men and creatures all live together happily, The few men who did not want to stay, were transported, by Aslan, into the world they came from-- the same world that the Pevensies live in. They also returned, but only after long goodbyes and many tears, especially for Peter and Susan, who knew they would never return.