The place is known locally and on early Ordnance Survey maps as Rathfran Abbey, though it was never an abbey in the strict sense: it was a friary, founded in 1274 and dedicated to the Holy Cross, home to the Friars Preachers, the Dominicans. The river beside it was not incidental to the choice of location. It gave the community access to fishing, trade routes, and the broader waters of Killala Bay, which stretches away to the east.

The friary's founder is uncertain, which is itself a quietly interesting detail for an institution of this size. It may have been Sir Richard d'Exeter, or it may have been Sir William de Burgh, Lord Justice of Ireland, whose wife came from the d'Exeter family. What is clearer is the friary's troubled later history. By 1438, a papal indulgence was being offered to anyone who gave alms toward its repair: it lacked a refectory, a bell tower, and a bell, and other buildings were described as ruinous. By 1458 it was again reported as impoverished and reduced by wars. In 1513, the Annals of Ulster record a killing on the premises, when Edmond Mac William de Burgo was murdered by his nephews inside the friary walls. After the Dissolution of the Monasteries, a lease of the site was drawn up in 1577, describing it as having one small house and a ruinous mill. In 1590, Sir Richard Bingham, Governor of Connacht, burned it. Even so, Dominican friars maintained a quiet presence in the surrounding area well into the eighteenth century: in 1756, five of them were recorded as living in a cottage in Mullaghnacroiste.

The fabric that survives is substantial and worth reading carefully. The church, over 33 metres long, retains walls that stand close to their full original height in mortared limestone rubble. A string course runs along the south wall of the chancel and terminates in a carved stone human head, placed on its side, greatly eroded now, which may have marked the original boundary between chancel and nave. A piscina, the small stone basin with a drain used for washing the communion vessels, sits in a finely moulded trefoil recess nearby, with twin basins and two shelves still intact. The side chapel added to the nave in the late fourteenth or early fifteenth century contains an east window of notable quality: a twin-light pointed lancet with quatrefoil tracery. Above the main west doorway, a small crucifixion plaque is carved in false relief beneath its own projecting hood. To the north of the church, the cloister and its surrounding domestic range are largely reduced to low walls, though one chamber at the south-east corner of the range still holds a partly intact vaulted roof, and beyond that, unusually, a second courtyard opens out, enclosed by another range of buildings now reduced to footings.