Mabinogion: first branch
The word "Mabinogi" originally designated only these four tales, which are really parts or 'branches' of a single work, rather than the whole collection.
Pwyll, Prince of Dyfed, is the hero of the first branch; his story is told in three distinct episodes.
In the opening part he changes places with Arawn, the king of Annwn, for one year. Annwn was the underworld, also identified as the island of Gwales or Grassholme on the Pembrokeshire coast.
Pwyll wins the title Head of Annwn, and Arawn's undying friendship, by uniting the two warring kingdoms of Annwn when he defeats Arawn's rival, King Hafgan in combat.
The second part of the tale concerns Pwyll's return from Annwn. After his men fail to catch the beautiful maiden Rhiannon on her ambling horse which magically can not be caught up with. However, Pwyll does so simply by asking her to stop.
Rhiannon, the first of several strong women in the Mabinogi, is betrothed to Gwawl. Nonetheless, she falls in love at first sight with Pwyll and proposes an elaborate plan to enable her to marry Pwyll rather than Gwawl.
Pwyll follows her plan - which relies on Rhiannon's knowledge of Gwawl's weaknesses, his pride and lust for her - and traps Gwawl in a sack that can never be fully filled. Pwyll's men beat Gwawl while he is in the bag, and Rhiannon is left free to marry Pwyll.
In the third part, Rhiannon bears Pwyll a son. The child disappears on the night after his birth, even though six women are appointed to keep watch on the new mother and her child.
The women plot to smear the blood of puppies onto Rhiannon's face and hands. Rhiannon is accused of killing the child, and is forced to sit outside the castle in Narberth, Pembrokeshire as punishment. She must tell her story to passers-by, and offer to carry visitors and pilgrims on her back into the court.
Meanwhile, Teyrnon Twryf Liant, lord of Gwent-Iscoed, finds the baby on his doorstep after chasing a monster away from his home. He raises the boy as his own and names him Gwri Golden-hair.
When the child's resemblence to Pwyll becomes apparent, he is returned to his parents. Rhiannon re-names him Pryderi (Worry) after all the anguish he's caused. Her punishment is ended.