In Prince Caspian, Caspian swears an oath to Asian that he will search for the seven noble lords who were sent on a suicide mission across the sea by the usurper Miraz.

For Narnians, swearing by Asian is very serious business; to actually swear an oath to Asian in the flesh is a matter of the utmost urgency. Thus, after taking a few years to settle the turmoil in Narnia caused by the civil war from Prince Caspian, Caspian undertakes a voyage to the east, trying to follow the lost lords.

Caspian was a very courageous and honorable young man in Prince Caspian; in The Voyage of the "Dawn Treader," he has grown taller and broad shouldered, to become the image of the ideal king. He leaves Narnia in the care of the Dwarf Trumpkin, the "Dear Little Friend" of Lucy, Peter, Susan, and Edmund in Prince Caspian. Trumpkin's honesty, faithfulness, and good sense will be put to good use in Narnia, freeing Caspian to fulfill his oath to Asian. The ship, the Dawn Treader, is manned entirely by volunteers; the Telmarine humans of Narnia have long feared the eastern sea, so the volunteers are people of exceptional courage, especially Reepicheep, the Chief Mouse.

First, the Dawn Treader sails north to the great seafaring community on the island of Galma, then east to the Seven Isles, where pirates lurk, then south toward the Lone Islands. On the way to the Lone Islands, the ship encounters three people in the water, and the crew fishes them out, discovering Queen Lucy, King Edmund, and the incredibly annoying Eustace, their cousin and devoted mischief-maker. The three children had been looking at a painting of a ship on the sea when they were absorbed into the painting and into the sea. This is only one of many wonders King Caspian and the crew of the Dawn Treader will encounter in The Voyage of the "Dawn Treader."