Slathissin gets a pretty good idea of the man's voice (a low, rich baratone) at about the same time as an Astartes in the colors if the Word Bearers, with a black right pauldron, rounds the corner, chainsword and bolt pistol in hand.
"What-" he snaps as he takes in the scene. He looks at Slathissin.
"One of Curze's faithless cowards, I would guess." He flicks his chainsword to life.