The exact address has never been pinned down, which is itself part of what makes this site so quietly telling. What survives is not a building or a plaque but a paper trail, a bureaucratic record that inadvertently preserved the names of the people and places the authorities were keeping watch on.

The key document is a government list of Catholic clergy compiled in 1618, during the reign of James I, a period when the practice of Catholicism was officially suppressed across Ireland under Penal legislation. A mass-house was simply a private dwelling or room adapted for the celebration of Mass, used in place of the Catholic churches that had been seized or closed. The 1618 list, cited by the historian Nicholas Donnelly in a 1904 study of Dublin's Catholic chapels, names among the most publicly known places of worship in the city "a back room of Mr. Plunkett, in Bridge Street." The phrasing is almost domestic in its plainness, which makes it more striking, not less. A back room. A name. A street. The historian J.T. Gilbert, writing in 1854, placed a mass-house on this street at around 1610, and the historian Colm Lennon later suggested it was located on Bridge Street Upper West, possibly within a structure known as Fitzsimon's Tower, a reference to one of the medieval tower houses that once dotted this part of the old city.

Bridge Street today is a busy road connecting the south quays to the older street network of the Liberties and the Coombe. There is nothing to mark the location of Mr. Plunkett's back room, and no certainty about which building, if any surviving, might correspond to Fitzsimon's Tower. For anyone curious enough to walk the street, the exercise is less about finding a monument and more about holding a particular kind of absence in mind. The 1618 list was compiled by people trying to suppress what they were recording. That the record survived, and that the name Plunkett and the street name Bridge are still legible in it, is a small, accidental form of preservation.