At 2.24 metres long and just a few centimetres thick at its thinnest point, it is a substantial piece of stone, worn smooth with age and cracked through the cross-head, its lower portion broken away entirely. What remains is still remarkably detailed: a seven-armed interlaced cross carved in false relief, meaning the decoration is raised against a recessed background rather than cut into the surface, with fleur-de-lys terminals at the cross-arms, a three-barred knop on the shaft, and heraldic imagery flanking the cross, a shield on one side and a lion rampant on the other.

The inscription running along the sinister border, that is, the left-hand side as you look down at the slab, is in Latin and cut in Black Letter script. When the historian William Carrigan transcribed it in 1905, he rendered it as commemorating Thomas Grace, described as a discreet man and formerly Rector of Callan, who died on 16 January 1583, with a closing prayer for his soul and the name Wat. Kerin, most likely the mason or the person who commissioned the stone. The lion rampant is a known emblem of the Grace family, connecting the deceased to one of the prominent Hiberno-Norman families of the region. Carrigan also recorded the initials T.G. above the lion, though these are no longer clearly visible, likely worn away over the intervening centuries. Carrigan did confuse this slab with another at the same site, noting damage to the top right of the monument that does not in fact exist here; the upper portion of this stone is entirely intact, and it is the lower section that is missing.

The date partially legible along the top border, mēs Januarii 1583, is one of the more immediate details for anyone crouching down to read the stone in the dim interior of St Mary's. The chamfered edges along the top and left side are worth looking for, a small refinement that speaks to the care originally taken over a slab that has since spent centuries underfoot.