Keinan is a timid young boy hidden away by his mother, Morgana, in a small cottage tower in the far away hills of the Kingdom of Memoria. He knows nothing of his mother’s life, only that she is often away, so he spends his time gardening, cooking, spilling things, cleaning, humming, and making toys out of wood. He has never met anyone else, and he wishes for a friend. One day, while his mother is away, his wish is granted when mischievous young knightess Cornelia, who goes by Cokkie, accidentally finds him in her search for adventure (or trouble!) They quickly become friends behind his mother’s back, and Cokkie returns to play everyday when she can sneak away from her lady’s maid schooling at the orphanage where she lives. At Cokkie’s request, Kei makes her a wooden sword.
One day, Cokkie’s curious nature leads the two of them to discovering Morgana’s secret unsent letters to the king which boasted that Kei is really the king and queen’s son and the true crown prince, and Morgana had switched him at birth with her own son who is now in the palace. When Morgana finds out they’ve learned the truth, she locks Kei up in his bedroom in the tower in an attempt to keep him and Cokkie apart, and to ensure that the world will never find out about him, and her secret stays hidden. But while she is away, Cokkie rescues him from his tower prison, and with the letters, they flee over the hills and through the woods to the capital city seeking more answers and to return Kei to his true home. But Morgana hires minions to pursue them: seven dwarves, three bears, three pigs, and a wolf. They encounter them in the Echo Fruit Forest, where the open fruit repeats words and sounds back to the sound maker. Through Cokkie’s firey, energetic spirit (and her wooden sword!) and Kei’s kind nature and toy-making skills, they outsmart or befriend those they meet along the way.
They finally make it to the city, and Cokkie’s antics get them into the castle where, to their surprise, they find Morgana already there as a member of the royal court. Morgana burns the letters, accuses them of trouble-making, and intimidates Kei. Using one of the echo fruits she swiped from the forest, Cokkie records Morgana’s conversation with Kei where she admits to the switch, and they manage to reveal the truth to the king and queen despite Morgana’s efforts to stop them. In anger, Morgana reveals to them all that her true son is also the king’s son. As it turns out, she and the king had been in love, but he chose to marry another woman instead of her. So in her fury, Morgana switched the boys to take revenge on him, and to put her own son on the throne instead of the queen’s son. In the end, Morgana is banished, both boys are adopted by the queen, and Cokkie is officially knighted.