Here's a recap of The Voyage of the Dawn Treader and the official movie trailer.
"Return to the magic and wonder of C.S. Lewis' beloved world - via the fantastic Narnian ship, the Dawn Treader. In this new installment of the blockbuster 'The Chronicles of Narnia' motion picture franchise, Edmund and Lucy Pevensie, along with their cousin Eustace, their royal friend King Caspian, and a warrior mouse named Reepicheep, find themselves swallowed into a painting and on to the Dawn Treader.
Their mission - on which rests the fate of Narnia itself - takes the courageous voyagers to mysterious islands and a river that turns to gold, to fateful confrontations with magical creatures and sinister enemies, and to a reunion with their friend and protector, the 'Great Lion', Aslan."