Prince Caspian was written by C.S. Lewis and published in 1951.
Narnia...the land between the lamp-post and the castle of Cair Paravel, where animals talk, where magical things happen...and where the adventure begins. Peter, Susan, Edmund, and Lucy are returning to boarding school when they are summoned from the dreary train station (by Susan's own magic horn) to return to the land of Narnia--the land where they had ruled as kings and queens and where their help is desperately needed. Troubled times have come to Narnia as it is gripped by civil war. Prince Caspian is forced to blow The Great Horn of Narnia, summoning the help of past heroes Peter, Susan, Edmund, and Lucy. Now they must overthrow Caspian's uncle, King Miraz, to restore peace to Narnia.