It is a direct sequel to the second branch, Branwen ferch Llŷr, and deals with the aftermath of Bran's invasion of Ireland and the horrific enchantment that transforms Dyfed into a wasteland.

Having honoured the last requests of his brother Bendigeidfran, by burying his head facing France so as to ward off invasion, Manawydan accompanies his friend Pryderi to the kingdom of Dyfed, where the latter is reunited with his wife Cigfa.

Pryderi and Manawydan travel to England to make a living from various trades, but are forced to leave one town after another to avoid conflict with other tradesmen who resented their superior skills.

Returning to Dyfed, Manawydan and Pryderi go hunting and, coming across a white boar, follow it to a huge, towering fort.

Cigfa weeps at the loss of her husband, but is comforted by Manawydan, and the two head off to England before being driven out, once again, due to their superior craftmanship.