Edmund Pevensie (Skandar Keynes), almost but not quite an adult, envies adult men. He tries to enlist in His Majesty's Army, but the recruiter, of course, catches him out with his fake I.D., especially when his sister Lucy (Georgie Henley) reminds him that he was supposed to help her with grocery shopping.Lucy envies any girl whom she thinks is prettier than she. The problem is that her only standards of beauty are her older sister Susan (Anna Popplewell), now in America, and any other girl who is hanging on the arm of a young man.Edmund and Lucy have another problem. Because the war still rages, they are evacuated once again. Only while Peter (William Moseley) and Susan are evaculated all the way to America, Edmund and Lucy are evacuated, not to Professor Digory Kirke's country estate (see The Lion, the Witch and the Wardrobe), but to the home of their obnoxious cousin, Eustace Clarence Scrubb (Will Poulter). Eustace has no social graces whatsoever and would like nothing better than to treat Edmund and Lucy as he would treat any of the arthropods in his considerable, and repulsive, collection.One afternoon, Lucy and Edmund are alone in the room that Edmund has to share with Eustace. They notice a painting on a wall--a painting of a ship on an ocean, a ship that looks very much like one of the ships they once sailed in the world of Narnia, where once they had reigned as a king and a queen. Only as they stare at the painting, the water seems to move, and the ship seems to come right at them. Eustace enters, and makes fun of them for indulging, as he sees it, in a flight of fancy. But then the seawater starts to *spill into the room.* Eustace, panicked, tears the painting off the wall, but that does no good. In the next instant, the room is full of water, rising until they are swimming in it. Soon they are underwater, and rising up to the surface of a real ocean. And there comes the ship, big as life!The crew of that ship pick them up at once. Edmund and Lucy discover, to their delight, that the ship is actually Narnian. The distinguished passenger on board is none other than King Caspian (Ben Barnes), with whom they had fought a successful war three years before (in Narnian time; see Prince Caspian). Eustace is thoroughly affronted, especially with a Talking Mouse (Simon Pegg) who protests that he was only trying to resuscitate him! To make matters worse, a walking, talking Minotaur (Shane Rangi) tells him that he is aboard the Dawn Treader, "the finest ship in the Narnian Navy!"Caspian welcomes Edmund and Lucy on board as honored guests. Then, after outfitting them both in Narnian clothing, he gives Lucy her dagger and medicinal cordial (and Susan's bow and arrows), and offers Edmund his old electric torch, which he had left behind.Now Caspian reveals his mission. He is looking for the Seven Lost Lords of Narnia, friends of his father's whom Lord Protector Miraz had driven into exile. They had fled to the Lone Islands, and no one has heard from them since. Caspian's mission: to rescue or recover them.Reepicheep the Talking Mouse has a mission of his own: he wants to travel to the literal end of the world, and find the country of Aslan (Liam Neeson), the lion-shaped God-King of the world of Narnia.Lucy thoroughly enjoys the sights and sounds of Narnia. Edmund and Caspian entertain the crew with a fencing match. Eustace stubbornly insists that he "never lost" his "sea legs." Eustace boasts that he will find the British Consulate, as if Britain even *has* a consulate in this world. But all this idle talk stops, as the Dawn Treader comes within sight of land: Narrowhaven, capital city on the largest of the Lone Islands, their immediate destination.Tavros the Minotaur, who obviously serves as boatswain on board, orders two longboats fitted out. In them, Caspian leads a landing party ashore. Edmund, Lucy, Eustace, and Reepicheep are all part of it. They find Narrowhaven deserted, and Caspian and the children go further inland to investigate. Inside an empty hall, they find ledgers showing purchases and sales--of slaves. Just then, the slavers rappel down ropes and attack. Lucy, Edmund, and Caspian handily fight off the attackers, but Eustace is easily seized, and used as leverage to capture all four of them. In the dungeon into which the slavers throw them, they find Lord Bern (Terry Norris), first of the Seven Lords, who has been a prisoner for many years. Bern recognizes Caspian as his king and tells him what has befallen Narrowhaven. Then they watch as the slavers take a cartload of very frightened slaves, load them into a longboat, and shove it out to sea--where an animated green mist suddenly appears, washes over them, and then disappears--with the slaves. Lord Bern tells Caspian that his six companions set out to find the source of the mist, and never returned. Bern has reproached himself ever since for not going with them.The next day, the slavers try to sell the children at auction. An apparent buyer shows up--who is actually Lord Drinian (Gary Sweet), captain of Dawn Treader, and enough men-at-arms to take over the town and set all the slaves at liberty. Eustace tries to steal away in a longboat, but succeeds only in decking another slaver who tries to kill him before the other Narnians show up.A distraught man of Narrowhaven name Rhince (Arthur Angel), seeking to find his wife Helaine (Rachel Blakely), who was on the last longboat devoured by the mists, signs on with Dawn Treader's crew. Lord Bern then retrieves a sword he has kept all this time, one of seven swords that Aslan gave to the Seven Lords. Bern gives this to Caspian, who then gives it to Edmund to use while he is in Narnia.Dawn Treader sets sail to go further east. Eustace keeps a diary, always assuming that everything around him is an illusion. And then on his first full night on board, he tries to steal water and food from the ship's rations. Reepicheep catches him at it, and the two fight a quick duel, Reepicheep with his sword, and Eustace with the first weapon he finds handy: a galley knife. The fight is almost one-sided, except that Reepicheep is trying more to train Eustace in swordfighting than to do him any real harm. Then Eustace falls over a bundle--that turns out to be a little girl, Gael (Arabella Morton), Rhince and Helaine's daughter, who desperately wants to find her mother. Captain Drinian says nothing about the attempted ration theft, and simply welcomes the little girl as "an extra crewmember." Lucy takes to Gael quickly and acts as her protector.Dawn Treader next fetches up at another apparently uninhabited island. Only this island *is* inhabited, by invisible men who hop about on one foot each--but are quite capable of abducting someone. They abduct Lucy and bring her into the garden of a mansion several yards inland (a mansion that is also invisible, and by the same means: a magic spell). They want her to go into this mansion, find a book of spells, and recite a spell to render them visible once again. Lucy reluctantly does so, especially after the voices tell her that they can neither read nor write.Caspian finds Lucy missing and awakens Edmund and the other members of the landing party (except Eustace, who sleeps on).Inside the mansion, Lucy finds the spell book, which she cannot open until she breathes upon it. She finds all sorts of spells inside, including a spell to make snow (she tries it, with success), and a spell to make one beautiful. She tears that page out, and then an angry lion's voice roars at her, rustling the pages. Then she hears Aslan's voice calling her name, after she looks into a mirror and sees her sister Susan's face. Now Lucy returns to the business at hand: she finds the spell to make things visible and says it. Just in time, too, for the inhabitants have captured Caspian and the landing party. When they become visible again, they let their guard down and tell all.Lucy reappears, and introduces Coriakin (Bille Brown), the master of the island. Coriakin apologizes for rendering the monopods ("Dufflepuds") invisible, saying that he had to protect them from "The Evil", i.e., the force behind the Green Mist. Now Coriakin has something to reveal: an animated, interactive chart of the eastern part of the Great Ocean. He tells Caspian, Edmund, Lucy, and Eustace that they must proceed to Aslan's Table, with a Blue Star to guide them, and lay upon it all of the Seven Swords of Aslan. But he also warns them: "You are all about to be tested." That applies equally to Caspian (who has always felt that he was not the king his father was) as it does to Lucy, Edmund, and Eustace.Dawn Treader then sets out again, this time sailing into a storm. Fourteen days effectively dampen everyone's spirits, except those of Reepicheep, who is hearty enough to accept anything as part of the adventure. Even Captain Drinian is reluctant, but Caspian insists on pressing on and reminds Drinian sharply that they have taken on a crewman and his daughter, who are very eager to find their loved one.During the storm, Lucy has the bad sense to try out the beauty spell. With the result that she becomes Susan, and finds herself with her brothers Peter (William Moseley) and Edmund in America. Problem: no such person as Lucy, and no Narnia, either. Now thoroughly frightened, Lucy awakes with a scream, to find herself face-to-face with Aslan. Aslan chides her for wishing herself away, and doubting her own value--for without Lucy, the Pevensies would never have found Narnia. Lucy, having learned her lesson, burns the beauty spell.The Green Mist briefly appears, and then moves out to the quarters that Edmund and Caspian share. Edmund wakes up to hear a voice he never wanted to hear again: that of his ancient temptress and cruel enemy, the White Witch of Narnia (Tilda Swinton). Then the Mist retreats when Lucy walks in on the boys to say that she could not sleep. Edmund knows why.The next day, the Dawn Treader puts ashore at yet another island. This one is uninhabited for real. Edmund, Lucy, and Caspian descend into a cave, where they find a pool of water with a golden statue at the bottom. Edmund tries to probe it with a broken-off branch--and the branch turns to gold in his hand. Then they realize that the statue is actually one of the Seven Lords, Restimar, now "aurified" and dead. They know that they must retrieve Restimar's sword--but Edmund is much taken with realizing that anything dipped into the pool turns to gold. He sees riches for himself, and Caspian sees a resource over which he, as king, should take dominion. Then the two start to argue, and only Lucy's intervention keeps the two from killing each other in a duel. And so they retrieve the sword and leave the pool alone.Eustace, meanwhile, goes off exploring on his own--and finds a rock defile filled with more treasure than he has ever seen in one place: gold, silver, and gemstones, all for the taking. He finds a skeleton (actually that of Lord Octesian) and puts on a gold bracelet that the skeleton had been wearing. That is a mistake.In the next scene, Caspian and Edmund set out to find Eustace, who they assume has strayed form camp. They find his clothing and diary, and fear the worst for him. They then recognize Octesian's remains and recover his sword. Then, out of nowhere, a winged, fire-breathing dragon swoops down from the mountains and alights on Dawn Treader's spar. Drinian leads his men-at-arms in a futile attempt to shoot the dragon off, and then Reepicheep climbs the mast and embeds his tiny sword into the dragon's talon. The dragon shrieks, jumps off, and flies back ashore--where he finds Edmund and Caspian, scoops up Edmund in his talons, and carries him inland, where Edmund reads this legend, burnt into the rocks: I AM EUSTACE.Edmund and Caspian realize the terrible truth: the dragon's treasure turned Eustace himself into a dragon. Lucy manages to relieve Eustace of Octesian's bracelet, which now hurts him terribly. Caspian observes that everyone in the world of Narnia knows that a dragon's treasure is enchanted, hence dangerous to collect or even to touch. Lucy, Edmund, Caspian, Gail, and Reepicheep agree to stay on the island overnight to keep Eustace company and decide how best to accommodate Eustace. Reepicheep actually warms to Eustace and tells him some of his favorite adventure stories. Eustace, unable to communicate, at least seems glad of the company. Reepicheep also suggests to Eustace that his transformation is a sign of an "extraordinary destiny" to come.In the next morning, the Blue Star appears to them. Dawn Treader embarks, with Eustace flying alongside. A mermaid tries to warn Lucy that they should sail no further; Lucy does not understand, and Caspian is determined to press on. Soon the ship is becalmed, and the men must fall to with their oars with grumblings from them of desiring to eat the dragon if the ship does not find land to resupply soon. However, Eustace wraps his tail around the ship's figurehead and takes it in tow. To that, the crew lets out a lusty cheer of approval upon realization that Eustace is now a valuable asset to the shipThat night, Dawn Treader lands at yet another island--Rhamandu's Island, where Aslan's Table is always spread. There the crew find three more of the Lords (Revilian, Argoz, and Mavramorn), not dead but fast asleep and tangled in their own beards. At Caspian's direction, they recover the swords that the Three Lords carried. They lay these, and the swords they brought with them, on the table--but they make only six. They still must recover one more.Then the Blue Star appears to them, and takes the form of a young woman--Liliandil (Laura Brent). She encourages them to eat freely of the fruit of Aslan's Table, and assures them that the three Lords are under a sleeping spell only for their own good, to stop them from killing one another, as they almost did. Liliandil then tells them that they must sail on to one more island: the Dark Island, source of the Green Mist and of every man's nightmare. There Lord Rhoop (Bruce Spence), carrying the last sword, walks that island, mad with fear. This will be their greatest hazard, for the island will make any man's nightmare take real form.Still they sail on to the island, with all hands armed. (Caspian gives his sword, that once belonged to Peter, to Edmund; Edmund gave up his sword at Aslan's Table.) Reepicheep struggles to give Eustace a pep talk, to remind him that, as a dragon, he has much better natural armor and weapons than any other hand aboard, and so should not flinch from battle.As Dawn Treader approaches the Dark Island, the Green Mist reaches out to it, though the men do their best to ignore it. Rhince sees a vision of his missing wife. Drinian sees a thick fog, that robs him of sight. Caspian sees a vision of his father, Caspian IX (Nathaniel Parker), dressing him down. Edmund sees the White Witch, who offers him the same thing that she once offered him many years before: to make him her king.Then they hear Lord Rhoop, shouting at them to keep off. Rhoop bears the Seventh Sword, as everyone thought he would. Rhoop is reluctant to come aboard, but Eustace simply flies to the island, scoops up Rhoop, and sets him on board. Rhoop acknowledges Caspian and warns Caspian that they must put out to sea at once and not think too much. But Edmund thinks of a Great Sea Serpent, which now takes form and attacks the ship.Eustace flies into battle and attacks the Serpent with all the fire he has--but the Serpent takes Eustace in his jaws, flings him this way and that, and throws him onto the rocks. Eustace recovers and blows more fire on the Serpent. Rhoop then foolishly throws his sword at the Serpent. He misses--and the sword embeds itself in Eustace' shoulder.Eustace flies off to Rhamadu's Island and makes a hard belly landing on the sand, as the Sea Serpent wraps itself around Dawn Treader, threatening to crush her. Edmund and Caspian seek to steer Dawn Treader toward the rocks, to ram the Serpent. Edmund challenges the Serpent, using Peter's old sword, while Caspian struggles with the wheel. Caspian's strategy is successful: they manage to stun the Serpent by slamming its head into a rock.Eustace, on the sand bar, wakes up. Aslan appears to him, and with a roar, burns off Eustace' dragon skin. Eustace wakes up, finding himself back in his old form, and with the Seventh Sword nearby. He takes it in hand and realizes that he is on Rhamandu's Island and can walk into the room of Aslan's Table. So while Dawn Treader's crew continue their desperate fight with the Serpent, and Edmund must struggle again with the temptation of the White Witch, Eustace races to the table and lays the last Sword on top of the other Six. The Mist tries to stop Eustace, but he disperses it with the sword.Edmund, of course, can't see Eustace doing this. But suddenly Peter's original sword, which he is carrying, turns bright blue. He realizes at once that the sword now is far more powerful than it ever was. So, though the White Witch (or her apparition) tries to dissuade him, he impales the Serpent with it. The Serpent dies and falls to the shallow bottom. The deep darkness lifts, and Dawn Treader is in daylight again. At Aslan's Table, the Three Lords awaken--and at the Dark Island, now no longer dark, every longboat of slaves that had gone to the Green Mist now comes out to meet Dawn Treader. Rhince and Gael are reunited with Helaine. Eustace then finds himself in the water, swimming to Dawn Treader. Reepicheep jumps in to rescue Eustace--and then they realize that the water is no longer sour, but sweet. Dawn Treader has now come within sight of Aslan's Country.Caspian, Lucy, Edmund, Eustace, and Reepicheep set out alone in a longboat to Aslan's Shore--which has a permanent, stationary breaker of surf on it. Aslan joins them there and informs them that their journey is at an end. Caspian, knowing that he would never return from an adventure into Aslan's Country, decides at the last instant to turn back, and go back to Narnia to govern it properly. Reepicheep is welcomed permanently into Aslan's Country, as has always been his destiny.Edmund says it's time for him, Lucy and Eustace to return home. Lucy understands that for her and Edmund, this is their last time in Narnia; they won't be returning. Aslan tells the Pevensies that they must now learn the name that Aslan bears on Earth, and their time on Narnia was intended to help them do that. Eustace is assured that he might be needed on Narnia once more, in the future.Aslan then sends Lucy, Edmund, and Eustace back to earth, back the way they came. They find themselves back in the room in Eustace' house. Eustace hangs the fallen painting back on the wall--and in it, Dawn Treader is sailing away from them. The film ends with Eustace' last diary record: that in the days that followed, the children spoke often of Narnia, and when the Pevensies leave, as they do once the war ends, Eustace will miss them. (But in a hint of the next intended sequel, Alberta Scrubb, Eustace' mother, shouts up to Eustace that a little girl named Jill Pole has stopped in for a visit.)