I don't know too much about Gwyn Evans other than that he wrote lots of lurid short stories for sensationalist magazines, like The Thriller, in the 1920s and 30s (see pic). He was also, I'm told, responsible for penning some of the better known Sexton Blake tales. In addition he authored a novel entitled The Homicide Club (1932) which was published in America. Apparently he lived in London where, having reacted against his strict Welsh Methodist upbringing, he became something of a booze-loving Bohemian. If you can fill in any more gaps in the life of Gwyn Evans please let me know.