The Voyage of the Dawn Treader
Lucy and Edmund Pevensie are staying with their Aunt and Uncle during the holidays. They don't look forward to the stay mainly because of their obnoxious cousin, Eustace. While spending some time alone in their room they are suddenly drawn, along with Eustace into Narnia. They end up on board a ship called the "Dawn Treader" with their good friend, King Caspian. They travel from that time on with Lord Drinian and Reepicheep the valiant mouse. They are on a quest to find seven Narnian lords whom Caspian's wicked uncle, Miraz, forced to sail away. Their first adventure happens on the Lone islands where they find the Lord Bern and furthermore reclaim the Lone Islands for Narnia. The second island they get to is called "Dragon island" because of the strange adventures of Eustace occur. He runs away to avoid work and ends up turning into a dragon. In this way is obnoxious Eustace reformed from being the selfish person he was previously. Only through Aslan though is he restored to humanity. They go through several other islands encountering a sea serpent, a river that turns things it touches into gold and a mysterious magician. Many of the characters exhibit great courage through this time and two of the Lords are accounted for as dead. They then go into the island where dreams come true, especially nightmares. On this island they finally meet the Lord Rhoop. They manage to escape it (through Aslan.) They then come to the last island before the end of the world. It is ruled by a star, who appears in human form called Ramandu. They find the last three lords here in an enchanted sleep. They find the only way to break the spell is to go to the end of the world and leave one of their crew there. Reepicheep volunteers to be that one. They do sail and then Aslan gives message to Caspian telling them to send Reepicheep and the children in a lifeboat to go on. Reepicheep leaves in a coracle to go to the world's end while the children go and meet Aslan in a grassy land. Aslan then sends them away telling Edmund and Lucy they will never return. 
BBC filmed one for television (merged with Prince Caspian). Walden Media is now preparing to film a new motion picture, this time separated from Prince Caspian. It is to be released on May 1, 2009.