The demon Lailoken, as old as time, is tricked by angels and trapped in a human body. He becomes Merlinus, a wandering wise man expert in magic, destined to work for good among humans, opposed by the Furor (Odin). An encounter with the unicorn, a spirit similarly earthbound, brings Merlinus to Ygrane, queen of the Celts, and she sets him a task to find her king, a man seen in vision and fated to be her love-match. Merlinus-Lailoken seeks and finds him: Theodosius, a stable worker. But Ygrane has commanded the demon-wizard to bring her a king, so Merlinus sets to work making one.