How Conchobor was Born and Became King of Ulster
Nes asked the druid Cathbad what the hour was lucky for. He replied it was lucky for conceiving a king, and swore that a son conceived then would be famous in Ireland forever. Nes and Cathbad therefore had relations. The son she bore was Conchobor. Cathbad raised him.

Fergus was King of Ulster, and he wished to marry Nes. She would only accept him if he allowed her son Conchobor to be king for a year. Conchobor was allowed to become king for a year, but Nes was clever. At the end of the year, she had persuaded the Ulstermen to not accept Fergus back.

How the Men of Ulster were Cursed with Labor Pains
Crunniuc mac Agnomain was a wealthy widower. One day, a fine woman walked into his house and stayed. The place flourished under her care. One day, there was great fair in Ulster. Crunniuc went, but the woman, being pregnant, did not. She warned him to be cautious in his speech, but he boasted at the fair that his wife could run outrun the king's chariot horses. The king immediately demanded she do so. The woman was fetched. She begged the crowd for compassion because she was going into labor, but to no avail. She told the king her name was Macha and that a curse would come on Ulster for what she was forced to do. She raced the chariot. As they reached the finish, she gave birth to a son and a daughter shrieking that every man who heard her scream would have labor pains when Ulster needed them most. All the men of Ulster there that day and their sons for nine generations after suffered the curse, except Cúchulainn and his father.

The Story of Deirdriu
Cathbad predicted that the daughter of the king's storyteller Fedlimid would be the most beautiful woman in the world and the cause of death in Ulster. The warriors wanted to kill her, but Conchobor had her raised in secrecy until she should be old enough to marry him. The girl, Deirdriu, met Noisiu, Uisliu's son, however, and fell in love with him. They ran off together with his brothers and eventually settled in Scotland. There they were threatened by the king who wanted Deirdriu himself. Conchobor offered them safe conduct home. Fergus, Dubthach, and Conchobor's son Cormac went surety (to stand in promise) for him. Conchobor had the brothers killed, Noisiu by the spear of Eogan mac Durthacht, who also killed Fergus's son Fiacha when he tried to protect Noisiu. Fergus, Dubthach and Cormac fled to the court of Connacht. Deirdriu killed herself.

The Birth of Cúchulainn
Deichtine, Conchobor's sister, was driving her brother's chariot as they hunted a great flock of destructive birds. When night fell, they came to a little house where a woman was about to give birth. Deichtine helped her deliver a baby boy. When morning came, everything had disappeared except the baby. Deichtine took the baby home with her, but he died. Deichtine was heartbroken. One of her servants brought her a drink of water. While she drank, a tiny creature flew into her mouth. She swallowed before she noticed it. That night, she dreamed a man came to her. He said he was Lug mac Ethnenn, a prince of the Síde, one of the magical beings who live in the fairy hills. The boy she had nursed was his son. She was now carrying him. He was to be called Sétanta. It soon became obvious Deichtine was pregnant so her brother married her off to Sualdam mac Roich. She was so upset at marrying him pregnant that she vomited up the being she had drunk. Soon, she was pregnant again by Sualdam. She had a boy. They named him Sétanta. Although the tradition of Cúchulainn's birth is contradictory, a rational explanation for his birth has never been expected.

The Pillow Talk
Medb and Ailill, the queen and king of Connacht, were talking in bed about who between them was the richer. Their possessions were counted; they were equal except that Ailill had a beautiful bull, Finbennach, the calf of one of Medb's cows that had gone over to Ailill's herd rather than belong to a woman. Medb asked Mac Roth if there was any bull its equal in Ireland. There was only one: the Donn Cúailnge in Ulster. Mac Roth was sent to borrow the bull for a year with the offer of a generous reward. Dáire, its owner, was pleased to lend the bull on such generous terms. Unfortunately, one of the messengers drank too much and announced that if the bull had not been lent, they would have taken it by force. Dáire was enraged and ordered them to leave.

The Muster of the Connacht Army
Ailill and Medb muster their army and wait for a favorable omen before setting out. The poetess and prophetess Feidelm tells Medb that the army will suffer enormous losses at the hands of Cúchulainn, repeating again and again, "I see them bloody. I see them red."

The Army Encounters Cúchulainn
Fergus, given command of the army, leads it astray to give the Ulstermen time to recover from their curse. Cúchulainn feels the imminent approach of the army and asks his father, Sualdam, to warn the people. Playing for time, Cúchulainn leaves a challenge to the Connacht army, but the army circumvents it. Again, he attempts to slow them down with a challenge: he placed a forked branch in the river and impaled the heads of four of the advancing warriors on it with a challenge that the army cannot pass until someone pulls the branch out with one hand. Fergus meets the challenge.

The Boyhood Deeds of Cúchulainn
Ailill asks Fergus Cúchulainn's age. When told that Cúchulainn is only seventeen, Medb scoffs that he could not be much of a warrior yet. Fergus recounts his boyhood deeds, including the story behind his name change. As a small boy, he killed a fierce watchdog that attacked him, and then guarded its owner's property until a new one could be reared. Hence came the name Cú Chulainn 'the hound of Culann.'

Cúchulainn's Challenge and the First Series of Combats
Cúchulainn puts a log in the army's path with a challenge that they dare not continue until a warrior leaps it in a chariot. Cúchulainn reluctantly kills his boyhood friend Fráech who had been sent against him. Fergus leaps the oak with his own chariot. Cúchulainn fights and kills all who come against him. The army pillages Ulster. Ailill suspects that Fergus and Medb are having an affair, and he sends his chariot driver to spy on them. He finds them sleeping together and steals Fergus's sword from its sheath. He returns with the sword to Ailill and confirms his suspicions. Ailill seems pleased by this: "She is justified. She does it to keep his help on the raid." He then tells the charioteer to keep the sword safe.

Bargain of the Single Combats
Cúchulainn takes his stand at the river Cronn, calling upon air, earth, and the river to help him. Maine, the son of Ailill and Medb, and thirty horsemen reach the river and Cúchulainn kills them all. These massacres continue until Fergus and Lugaid mac Nois Allchomaig organize terms of engagement favorable to Cúchulainn.

The Escape of the Bull, the Bargain of the Single Combats, and the Morrigan
Medb sets out with a third of the army to find the bull and lay waste to Ulster. Cúchulainn meets her cowherd Buide mac Báin with the stolen Bull of Cooley. Cúchulainn kills Buide, but Medb's men get the bull to their camp. Cúchulainn fights warrior after warrior. In the midst of his struggles, the Morrígan, in the shape of a young woman, comes and offers herself to him. He spurns her. She swears to hinder him. He promises to wound her. She will carry the marks forever unless he gives her a blessing. He continues to fight whatever champions they send against him. When Lóch, his foster brother fights him, three times the Morrígan hinders him and is wounded. Fergus encourages Briciu to taunt the flagging Cúchulainn to keep his anger up in the fight. Cúchulainn feels his own need for help. He kills Lóch, but is exhausted. The Morrígan appears now as an old woman milking a cow. He asks for a drink of milk. She gives him three and with each he blesses her and she is healed. Medb organizes an ambush, but Cúchulainn kills the warriors. She offers her daughter to him, but he cuts the girl's hair and leaves her on a pillar stone.

Respite for Cúchulainn
Laeg spots a fine-looking man coming towards them. Cúchulainn recognizes him as one of the síde. The man identifies himself as Cúchulainn's father from the fairy hills, Lug mac Ethnenn. Cúchulainn admits, "My wounds are heavy. It is time they were let heal." Lug tells him to sleep. He tends his son's wounds. While Cúchulainn sleeps, the boys of Ulster come to his aid and are, to Cúchulainn's sorrow, slaughtered after a brave fight. Cúchulainn orders out his sickle chariot, 'every angle and corner, front and rear was a tearing place,' and in a frenzy, rages through the army encamped against him.

The Single Combat of Ferdia and Cúchulainn and the Fight of Cethern
An Ulster warrior, Oengus, comes and hurls stones at the Connacht army until he is slain. Trying to find another warrior to fight Cúchulainn, Medb approaches Fergus. He refuses to fight his foster son. However, he faces Cúchulainn, asking him to retreat a step before him if he gives ground at another time when asked by Cúchulainn. He agrees. There is more fighting in which Cúchulainn is victorious.

Fíacha mac Fir Febe, an Ulster exile, goes to Cúchulainn's aid in one fight. Medb works on Cúchulainn's foster brother and closest friend, Ferdia, telling him Cúchulainn has slandered him. The two fight over four days. Finally, Cúchulainn gives Ferdia a mortal wound, but laments over his lost friend. The Ulster warrior Cethern arrives, attacks the army and then retreats to Cúchulainn with a litany of his wounds. He kills doctor after doctor until Conchobor's doctor Fingin arrives. He examines his wounds from a safe distance, and tells him he can either stay still for a year and live or have three days of strength to fight before dying. He chooses the latter and dies fighting.

Fintan and the Death of Finnabair
Fintan, father of Cethern, arrives to avenge his son. His other son is taken prisoner and returned on condition that Fintan not attack Ailill's army until the final battle. Rochobad Rigderg arrives to help Cúchulainn, but Ailill arranges a trap for Rochobad, baited with Finnabair, who has told her parents how much she loves him. Her parents agree to allow Finnabair and Rochobad to sleep together if Rochobad gives them a truce until Conchobor arrives.

The Warning of Súaldaim and the Muster of the Men of Ulster
Súaldaim goes to his son's aid. Cúchulainn sends him to warn the Ulstermen to come immediately if they hope to punish the invaders. Súaldaim reports "men are slain, women carried off, and cattle driven away." He falls and is decapitated by his own shield, but his head repeats the warning. Conchobor vows to crush the raiders and bring back their booty.

Ailill asks Mac Roth if he can see the Ulstermen approaching. He says they are coming on like a lightning filled mist. He goes out again and sees the Ulster camp and comes back with descriptions of the men and troops he has seen. Fergus identifies them for the king. A truce is arranged until the next morning. The Morrígan appears to prophesy the coming slaughter.

The Battle of the Armies and of the Two Bulls
The battle begins. Ailill and Medb beg Fergus to join the fight and give him back his sword. He cuts through the Ulstermen and confronts Conchobor, but is restrained by Cormac who begs him to remember his own people. Cúchulainn leaves his sick bed, arms and confronts Fergus, demanding that he keep his promise to retreat before him. Fergus takes the Ulster exiles out of the battle. The men of Leinster and Munster follow them. Cúchulainn catches up with Medb, but spares her. Fergus observes that the outcome of the battle is what one would expect when the herd follows a mare.

The following morning the survivors gather to watch the fight between the two bulls. The Donn Cúailnge defeats Finnbennach, littering the landscape with pieces of Finnbennach's body. The places where they fight give rise to place names (places where important events occurred). The Donn Cúailnge finally dies at Druim Tairb.