TE I

1. The story begins with the conception of Aengus by the Dagda and Boand, wife of Elcmar. Aengus is fostered by Midir, and when he grows up takes possession of Brug na Boinne from Elcmar.
2. Midir visits Aengus, but is blinded by a sprig of holly thrown by boys playing the Brug, and after he has been healed by the physician Dian Cecht, he demands compensation from Aengus: among other things, the hand of the most beautiful woman in Ireland. He has already identified this woman: Étaín, daughter of Ailill, king of the Ulaid. To win her for Midir, Aengus has to perform various tasks for Ailill, including clearing plains and diverting rivers, as well pay her weight in gold and silver. Midir takes Étaín as his wife.
3. However, Midir's first wife, Fúamnach, out of jealousy, turns her into a pool of water, out of which, as it evaporates, emerges a beautiful purple fly. Midir knows the fly is Étaín, and she accompanies him wherever he goes. But Fúamnach conjures up a storm which blows the fly away, and she drifts for seven years before landing on Aengus's clothing, exhausted. Aengus makes her a crystal bower which he carries around with him, until she returns to health. Fuamnach conjures up another storm and blows her away from Aengus, and after another seven years she lands in a golden cup in the hand of the wife of Étar, a warrior of the Ulaid, in the time of Conchobar mac Nessa. Étar's wife drinks from the cup, swallows the fly, and becomes pregnant. Étaín is reborn, 1,012 years after her first birth. Meanwhile, Aengus hunts down Fúamnach and cuts off her head.

TE II

The High King of Ireland, Eochu Airem, seeks a wife, because the provincial kings will not submit to a king with no queen. He sends messengers to find the most beautiful woman in Ireland, and they find Étaín. He falls in love with her and marries her, but his brother Ailill also falls for her, and wastes away with unrequited love. Eochu leaves Tara on a tour of Ireland, leaving Étaín with the dying Ailill, who tells her the cause of his sickness, which he says would be cured if she gave the word. She tells him she wants him to be well, and he begins to get better, but says the cure will only be complete if she agrees to meet him on the hill above the house, so as not to shame the king in his own house. She agrees to do so three times, but each time she goes to meet him, she in fact meets Midir, who has put Ailill to sleep and taken his appearance. On the third occasion Midir reveals his identity and tells Étaín who he really is, but she does not know him. She finally agrees to go with him, but only if Eochu agrees to let her go.

TE III

Later, after Ailill has fully recovered and Eochu has returned home, Midir comes to Tara and challenges Eochu to play fidchell, an ancient Irish board game, with him. They play for ever increasing stakes. Eochu keeps winning, and Midir has to pay up. One such game compels Midir to build a causeway across the bog of Móin Lámrige: the Corlea Trackway, a wooden causeway built across a bog in County Longford, dated by dendrochronology to 148 BC, is a real-life counterpart to this legendary road.^[6] Finally, Midir suggests they play for a kiss and an embrace from Étaín, and this time he wins. Eochu tells Midir to come back in a year for his winnings, and gathers his best warriors at Tara to prepare for his return. Despite the heavy guard, Midir appears inside the house. Eochu agrees that Midir may embrace Étaín, but when he does, the pair fly away through the skylight, turning into swans as they do so.

Eochu instructs his men to dig up every síd (fairy-mound) in Ireland until his wife is returned to him. Finally, when they set to digging at Midir's síd at Brí Léith, Midir appears and promises to give Étaín back. But at the appointed time, Midir brings fifty women, who all look alike, and tells Eochu to pick which one is Étaín. He chooses the woman he thinks is his wife, takes her home and sleeps with her. She becomes pregnant and bears him a daughter. Later, Midir appears and tells him that Étaín had been pregnant when he took her, and the woman Eochu had chosen was his own daughter, who had been born in Midir's síd. Out of shame, Eochu orders the daughter of their incestuous union to be exposed, but she is found and brought up by a herdsman and his wife, and later marries Eochu's successor Eterscél and becomes the mother of the High King Conaire Mór (in Togail Bruidne Dá Derga she is named as Mess Búachalla and is the daughter of Étaín and Eochu Feidlech).^[7] The story ends with Eochu's death at the hands of Sigmall Cael, Midir's grandson.^[8]