While illegally street racing in the underground tunnels of Glasgow, four Harley Davidson riders make a horrifying discovery. A dead man left in the darkness, hands together on his chest as if peacefully laid to rest. The cause of death unclear, the only clues being a half glass of red wine, and a partially eaten chunk of bread by his side that echo the ancient religious practice of sin-eating. Called to the scene, forensic scientist Rhona MacLeod is perplexed by the lack of evidence. But when another body is found nearby her flat set up in the same manner, she fears a forensically aware killer stalks the city and is marking his victims with his unique signature. Even more worryingly, the killer appears to be using skills he could have learnt while attending one of her forensic science lectures at Glasgow University. There are signs that Rhona is being targeted. That he is playing with her and the police, drawing them into a deadly race against time to identify him before any more bodies are found . . .