Colum is the lord of Sevenwaters, a seventh son of a seventh son. Colum should not have inherited his family home, but each of his six brothers was killed in combat protecting their homeland. Colum should have become a druid, but he fell deeply in love and was passed over. Colum's love for his wife was absolute. Therefore, when she died Colum was devastated, surviving only by throwing himself into the running of his land. Colum is rarely home, and when he is he is a strict, dispassionate father. Colum wants his sons to be warriors and is deeply unhappy when Finbar suggests Britons are human and should not be treated as enemies.
Colum falls under the spell of an evil witch, lady Oonagh, and brings her home to become his wife. Colum is so deeply under the spell of this woman that he will not heed the warnings of his sons or his priest. When Colum marries lady Oonagh, bad things begin to happen at Sevenwaters, culminating in the disappearance of all seven of Colum's children. Colum is so devastated by this that he goes insane. However, when the children return, Finbar helps him to restore his sanity.