Suspicious deaths in a squalid London thoroughfare prompt a police inquiry that uncovers poisoned objects and perplexing clues. Inspector Whyland pursues leads and legal proceedings begin, while the analytical Dr. Priestly applies scientific reasoning to reassemble the evidence: a poisoned pipe-stem, a hypodermic needle, skeletal and material traces, and a contested will. Investigations range from inquests and a dramatic trial to discoveries at country locations, and the careful exposition of forensic detail and motive brings the mystery to a conclusive explanation.