Rilian is the only son and heir to the throne of Caspian X was born in 2325 NT. His mother, daughter of a retired star named Ramandu, was Caspian’s bride who he brought home from the Eastern end of the world in 2310 NT. One May morning in 2345 NT when he is 20 years old his mother, the queen, dies in the Northern parts of Narnia from the bite of a large serpent "green as poison". Rilian rides north every day for a month afterward wanting to avenge his mother by killing the reptile. His friend, Lord Drinian, questions the prolonged vendetta of the prince and is surprised to find that the prince had forgotten about the serpent and now rides out to the North to see "the most beautiful thing that was ever made." Drinian rides out with him the next day and beholds at noon a tall, beautiful lady dressed in a thin, green garment. He also sees that Rilian is staring at her "like a man out of his wits" until she disappears. It also strikes Drinian that the lady is evil. Drinian doesn’t tell the king - not wishing to be a tell-bearer. The next day, Rilian doesn’t return from his outing. His friend, Lord Drinian, suspects that the beautiful green-kirtled lady he saw in the woods is the reason for Rilian’s disappearance. Over thirty champions of Narnia went searching for him only never to return. King Caspian then forbade searching for his son because he didn’t want "all the bravest Narnians destroyed in the search for his son."
Unbeknownst to any Narnians, Rilian was not dead, but enchanted. The beautiful green lady whom he had seen in the Northern woods had captured him and taken him to her kingdom in Underworld. This witch plans to dig upward toward Narnia and overthrow it with Rilian at the head of her army of enchanted Earthmen. Rilian remembers nothing of who he was before he came to the Queen of Underworld’s kingdom. Rilian assumes that she rescued him from "some evil enchantment" since he goes into ravings at a certain time every evening. During this time, he is bound in a silver chair while the Queen alone attends him. Rilian remembers nothing of these fits but wakes from them only a little fatigued. What actually happens is that during that time he remembers that he is Rilian and struggles to free himself from the deep enchantment the Witch has bound him in. One evening, while the Queen is at the diggings, Rilian is awakened from his ravings and finds his bonds cut. Immediately, retrieves his sword from a table and attacks the silver chair, smashing it to smithereens. "Lie there, vile engine of sorcery," he cried "lest your mistress should ever use you for another victim." Looking around Rilian notices his deliverers - a Narnian Marshwiggle, a young boy, and a small girl. Rilian learns that he has been enchanted for ten years and that these three were sent by Aslan to find him.
The Witch then enters and perceiving what has happened begins to lull them all into an enchanted sleep, all the while convincing them that Overworld, Narnia, the sun and Aslan never existed. Puddleglum saves them all by stomping the fire in which she had thrown a sweet-smelling powder. Furious, the Green Lady turns into a huge green serpent and tries to kill the Prince. The men however, succeed in killing her, only to set off a chain of events that lead to the end of her kingdom. The Narnians decide to make for the diggings after being told by a gnome named Glog that "a few strokes of a pick" separated them from the surface. When they reach the end of the tunnel, Puddleglum hoists Jill up through a hole in the roof. Dwarfs, Fauns and Dryads help her out and dig out the others. The next day Rilian meets with his aged father who had come back early from an eastward journey because Aslan had told him that Rilian would be waiting for him. After embracing and blessing his son, King Caspian dies, leaving Rilian at age 30 to rule Narnia. One notable descendent is Tirian, the last king of Narnia who is 7th in decent from Rilian.