Pryderi, son of Pwyll and Rhiannon, is kidnapped on May Day when just a baby. On the same night every year, Teyrnon, lord of Gwent Is Coed, would lose a foal in mysterious circumstances, and one year, he stays up all night to protect his newest foal. When he sees a claw reaching out to kill the foal, he swings at it with his sword and a baby falls out.

He and his wife raise the child until he has grown strong, and eventually they notice the striking resemblance between him and Pwyll lord of Dyfed. He is returned to his birth parents, and as a result of the worry he has caused them over the years, they name him Pryderi son of Pwyll.