Once in Matholwch's kingdom, Branwen gives birth to a son, Gwern, but Efnysien's insult continues to rankle among the Irish and, eventually, Branwen is mistreated, banished to the kitchen and beaten every day. She tames a starling and sends it across the Irish Sea with a message to her brother Bran, who sails from Wales to Ireland to rescue her with his brother, Manawydan and a huge host of warriors, mustered from the 154 cantrefs of Britain. The Irish offer to make peace and build a house big enough to entertain Bendigeidfrân but hang a hundred bags inside, supposedly containing flour but actually containing armed warriors. Efnisien, suspecting treachery, reconnoitres the hall and kills the warriors by crushing their skulls. Later, at the feast, Efnysien, again feeling insulted, murders Gwern by burning him alive, and, as a result, a vicious battle breaks out. Seeing that the Irish are using the cauldron to revive their dead, he hides among the Irish corpses and is thrown into the cauldron by the unwitting enemy. He destroys the cauldron from within, sacrificing himself in the process.