When a young queen falls mysteriously ill, her children, Megan and Owen, are sent deep into the forest in search of her only cure, the legendary unicorn. The great magician Merlin helps them on their quest. With riddles and the unicorn's song the children travel to the magical isle of Avalon where they must decide what will truly cure their mother, King Arthur's powerful sister Morgan-le-Fay, or the healing touch of the unicorn.