Lucy and Edmund are spending a dreary holiday with their cousin Eustace Clarence Scrubb, who is a rather dour and mean spirited little boy. They are unexpectedly drawn into Narnia when a painting of a ship on the wall of Lucy's room comes to life, and the three children fall into the ocean to be rescued by the Dawn Treader.

Once safely on board, Lucy and Edmund are greeted by their friend Caspian (now King Caspian) who has undertaken a quest to find the seven lost Lords of Narnia, as he had previously promised to Aslan. Lucy and Edmund are delighted to be back in Narnia, but Eustace is less than enthusiastic. Reepicheep is also on board, as he has vowed to find the seas of the "utter East".

Joining forces once again with their royal friend Prince Caspian and the warrior mouse Reepicheep, they are whisked away on a mysterious mission to the Lone Islands, and beyond. On this bewitching voyage that will test their hearts and spirits, the trio will face magical Dufflepuds, sinister slave traders, roaring dragons and enchanted merfolk. Only an entirely uncharted journey to Aslan's Country – a voyage of destiny and transformation for each of those aboard the Dawn Treader – can save Narnia, and all the astonishing creatures in it, from an unfathomable fate.