The King of Ireland is on a hunting expedition. At a lake he is distracted by a swan who is constantly casting away one of her young. Perplexed, the King seeks council with his druid who explains that in nature any living creature will send its thirteenth offspring into the world to fend for itself. The King himself has thirteen beloved sons and the druid informs him that he is no exception to these natural laws. With a broken heart he closes the castle gate on his eldest son who then rides off into the Eastern World disguised as a cow herder. Here he finds favour with the Eastern King who needs a cowhand. Soon the prince has to battle with fierce giants, great warriors and a giant sea serpent to stand any chance of winning the Eastern Princesses hand in marriage.

Bhí Rí na hÉireann amuigh ag seilg nuair a tháinig sé ar eala a bhí ar snámh amuigh ar loch. Bhí trí éinín déag ag an eala agus d’aithin an Rí go mbíodh sí i gcónaí ag bualadh an cheann deiridh de na héiníní agus á thiomáint uaithi. Chuir sin an oiread iontais air gur bhrostaigh sé abhaile chuig an chaisleán gur chuir fios ar a fhear feasa, an Sean-Dall Glic. Nuair a chuala sé an scéal sin, mhínigh an Sean-Dall Glic don Rí

‘An uile neach beo a mbeirtear trí cinn déag de pháistí óga dó, ní mór dó an tríú ceann déag acu a ruaigeadh amach sa saol, chun bheith ag seiftiú dó féin. Maidir leatsa,’ ar seisean le m’athair, ‘tá triúr mac déag agat agus caithfidh tusa an rud céanna a dhéanamh.’

Agus sin mar a tharla, go tromchroíoch dhún a athair, an Rí geata an chaisleán ar a mhac is sine. Chuir sé air seanéadaí gioblacha agus thug sé a aghaidh ar an Domhan Thoir. Fuair sé obair ag an Rí ag tabhairt aire do na heallaigh. Ón bhomáite sin ar aghaidh, b’éigean don phrionsa, i mbréagriocht troid le fathaigh fíochmhaire, gaiscígh iontacha agus ollphéist mhór ghránna le croí an banphrionsa a bhaint.