The current release date of the movie was supposed to be on December 14th, 2007, Disney decied to move it several months later to avoid competiton with another fantasy film called, "The Water Horse". The Chronicles of Narnia: Prince Caspian is the 2/7 in the Narnia series written by C.S. Lewis. Here's a short description of the movie.
Time flies much faster in the magical world of Narnia than it does in our world, so the next time the Pevensey siblings (Peter, Susan, Edmund and Lucy) travel there from an English train station, they find themselves on an island during a time when Narnia is ruled by the Wicked King Miraz. The Pevenseys ally themselves with the young Prince Caspian, and the mighty lion Aslan, in an effort to revive Narnia's past and overthrow the evil king.