Ralph Comer – The Mirror Of Dionysos (Tandem, 1969: USA as To Dream Of Evil, Award, 1969)
Blurb:
The flicker of moonlight in the mirror was hypnotic, and a sudden wave of nausea swept over him. The mirror changed to a kaleidoscope of whirling colours, swelled to a vortex into which he felt himself failing …..
He stood on the sand, and a faint moon lit the arena with a gloomy radiance. The beginnings of fear caressed the nape of his neck as he recognised the cause of the elongated shadow in the middle distance. With an infinitely painful and shuffling gait, the shadow — man or animal, he could not tell — ambled across the sand towards him. Every fibre of his body, every nerve and sinew, willed themselves to flee from the stumbling horror, which, as it closed on him, raised its mutilated head and called out a travesty of his name.
See also The Mirror Of Dionysos thread on Vault forum