An entry in the Red Book of Clanranald, the medieval Gaelic chronicle, reads: "Beathag, daughter of Somerled, was a religious woman and a Black Nun. It is she that erected Teampall Chairinis in Uist." Black Nun was the colloquial name for an Augustinian, after the dark habit. Bill Lawson has noted the only complication in the ascription: Beathag was prioress of Iona around 1203, when the Islands were still under Norse rule, though many of the Norse families had become Christianised by then. Beathag - sometimes anglicised as Bethoc - was a half-sister of Reginald, Somerled's son, and held authority within the most prestigious religious community in the Hebrides at a time when prestige was still measured in conversions.

Amie mac Ruari was the last MacRory heir, sole surviving descendant of one of the great branches of Somerled's line. She married John of Islay, the first Lord of the Isles, and brought him the lordship of the Uists as her inheritance. A decade later he divorced her to marry the daughter of the High Steward of Scotland - a politically more advantageous match. The divorce settlement, depending on which version one reads, was either Amie's vindication or her consolation. She received lands, kept her dignity, and is said to have spent the rest of her life rebuilding and enlarging Teampull na Trionaid. In 1389 her son Godfrey confirmed a grant his great-aunt Christina had made to the Abbey of Inchaffray from Sancta Trinita in Chairinis - confirming, in a single document, that the original gift was already at least two generations old.

During the Scottish Reformation in the sixteenth century, the families of Roman Catholic priests, tacksmen, and clan chiefs all attempted to claim church lands for themselves. The convent's institutional life ended. The walls began their slow conversion from monastery into ruin. The Battle of Carinish, fought near the convent in 1601 between Clan MacDonald of Sleat and Clan MacLeod of Dunvegan, made the surrounding land briefly violent again. The roofs went. The decorated stonework weathered or was carried off. The stories survived in oral tradition longer than the building did as a functional space - the persistent claim that this had been a college of learning, even the first university, repeated through the centuries by people who remembered something of what had once been here.

Rev. Kenneth MacLeod of Gigha, who collaborated with Marjory Kennedy-Fraser in collecting Scottish Gaelic songs, recorded one local memory in 1907: "In the early days of the nineteenth century, the North Uist people, on a day still spoken of, reverently laid in their Temple of the Trinity an unknown body washed ashore by the flowing tide; at twilight a mysterious-looking barge glided into the bay, three of its crew marched up silently to the temple, opened the newly-made grave, carried off the body, and then disappeared forever into the darkness and the great open sea." Whatever happened that day - if anything did - the local people remembered it. The ruins are now protected as a scheduled monument, the walls open to the sky, the stories still circulating quietly among those who know them.