The Irish king Matholwch sails to Harlech to speak with Brân the Blessed high king of the Island of the Mighty and to ask for the hand of his sister Branwen in marriage, thus forging an alliance between the two lands. Bendigeidfran agrees to Matholwch's request, but the celebrations are cut short when Efnysien, a half-brother to the children of Llŷr, brutally mutilates Matholwch's horses, angry that his permission was not sought in regards to the marriage. Matholwch is deeply offended until Bran offers him compensation in the form of a magic cauldron that can restore the dead to life. Pleased with the gift, Matholwch and Branwen sail back to Ireland to reign.