Rather than lying flat over a burial as intended, the upper half of the slab, roughly 55 by 52 centimetres, was repurposed as a quoinstone, one of the cornerstones used to reinforce a building's angles, and set into the north-east corner of the vestry. Anyone who happened to glance at the right external corner at the right moment might notice something unusual: carved decoration and lettering pressed against the masonry, a funerary monument absorbed into the building's own bones.

The slab dates to the 13th or 14th century and is cut from fossiliferous limestone, the local Kilkenny black marble flecked with the compressed remains of ancient sea creatures. Its carved face shows a floriated cross, meaning the arms terminate in leaf or flower forms, rising from a small orb above the shaft. The triangular spaces between the arms of the cross, known as spandrels, are filled with incised circles, and the original chamfered edges survive along the left and right sides of the cross-head. The top and base of the slab, however, have been cut away, truncated at some point when the stone was reused, which is why only the upper portion remains. Below the cross-head, on the right-hand side, an inscription in Roman capitals survives. It reads: R R I B. Whether those letters represent an abbreviated name, a dedication formula, or something else entirely is not recorded, and the abbreviation has so far resisted definitive interpretation, which gives the slab a quietly unresolved quality that no amount of architectural reuse has managed to erase.