Hide and Seek by Ian Rankin (St Martin's Paperbacks 1990)

Hyde's Club. Named after Robert Louis Stevenson's villain, Edward Hyde, the dark side of the human soul. Hyde himself was based on the city's Deacon Brodie, businessman by day, robber by night. Rebus could smell guilt and fear and rank expectation in this large room. Stale cigars and spilt whisky, splashes of sweat. And amongst it all moved Ronnie, and the question which still needed to be answered. Had Ronnie been paid to photograph the influential and the rich - without their knowing they were being snapped, of course? Or had he been freelancing, summoned here only as a punchbag, but stealthy enough to bring a hidden camera with him? The answer was perhaps unimportant. What mattered was that the owner of this place, the puppet-master of all these base desires, had killed Ronnie, had starved him of his fix and then given him some rat poison. Had sent one of his minions along to the squat to make sure it looked like a simple case of an overdose. So they had left the quality powder beside Ronnie. And to muddy the water, they had moved the body downstairs, leaving it in candlelight. Thinking the tableau shockingly effective. But by candlelight they hadn't seen the pentagram on the wall, and they hadn't meant anything by placing the body the way they had.
Rebus had made the mistake of reading too much into the situation, all along. He had blurred the picture himself, seeing connections where there were none, seeing plot and conspiracy where none existed. The real plot was so much bigger, the size of a haystack to his needle.