Connla, the son of Ulster champion Cú Chulainn and Scottish warrior woman Aoifé was raised alone by his mother in Scotland. Before he returned to Ireland after training with Aoife’s rival, her warrior sister Scáthach, Cú Chulainn requested that his son be sent to him when he was old enough. However, Cú Chulainn puts three geas on Connla.
A geas is a condition that can be both a curse and a gift. If a geas is violated it will result in dishonor or death. If a geas is observed it brings the one bound by a geas great power. An example is when Cúchulainn had a geas to never eat dog meat, but also bound by a geas to eat any food offered to him by a woman. So when a hag offered him dog meat, he had no way out of breaking a geas and this led to his death.
Connla first geas was that he could not turn back once he set off on his journey. His second geas was that he must never refuse a challenge, and the third geas was that he was to tell no-one his name.
When he come of age, Connla set off on his journey and eventually arrived in Dún Dealgán, now known as Dundalk (meaning "Dalgan's fort"), in County Louth, Ireland, and home to his father. There he is met by the warrior Conall Cernach, who asked his name. When he refused to answer, Conall challenges Connla to a duel. Connla quickly defeats Conall with his superior warrior skills and both disarmed and humiliated him.
Cú Chulainn approached Connla and asked him the same question. Thinking it could be his father, Connla cleverly responded "If I were not under a command, there is no man in the world to whom I would sooner tell it than to yourself, for I love your face."
However, ignoring the praise, Cú Chulainn challenged Connla to a duel. The two skilled trained warriors fight with great skill. In fact, being matched in skill, Cú Chulainn transformed himself using his “warp spasm”. Connla instantly realised this was his father, and lay down his weapons before him.
Cú Chulainn's wife Emer, realised who Connla was and tried to warn Cú Chulainn that he was fighting his own son. However, in a frenzy Cú Chulainn cast Gáe Bulg into Connla and he is fatally wounded. Before he passed into the next life, Connla finally spoke his name and then praised Ireland's mighty warriors. When Cú Chulainn realised he had killed his own son, he is stricken by grief. It marked the beginning of the end for Ulster’s champion.