The lone figure is a tall man in a hooded robe. What at first looked like a lantern from a distance, looks like some type of strange one foot diameter orb of metal and resembling a eye. The purplish glow is emanating from the iris of the eye.
The man stops. Looks at the fading view of Keltos' previous planar location, and then turns and faces directly the invisible Keltos trying to climb up on one of the buildings surrounding the cobblestone plaza. The emanation extends outward, like a beam of light from a hooded lantern, and outlines the invisible Keltos in purple.
The expression on the man's face is one of barely contained amusement.