The shadow on the spark

A physician returns from abroad to discover a close friend has died after an emergency amputation; official testimony attributes the death to surgical shock and blood poisoning while a large life insurance policy suggests motive. Doubting the accepted account, the physician applies medical knowledge and forensic experiments to challenge the inquest, untangling relations among the deceased, an adopted son, and a young secretary. Strange incidents, including a hunchback destroying papers, and an ingenious scientific stratagem complicate the investigation and illustrate how circumstantial evidence can mislead until careful analysis reveals an alternative explanation.