Detective Murdoch finds himself investigating his fellow policemen when a skeleton is found under concrete while Station 4 is undergoing renovation. Dr. Grace determines that the victim was an adult male with the cause of death most likely a blow to the temple. The concrete floor had been poured in 1881 and records indicate that Chief Constable Giles was the detective at Station House 4 at that time. Others who worked there include retired Chief Constable Stockton who was the station's inspector and Brackenreid, who was a uniformed officer. Murdoch and Crabtree soon determine that the victim was Constable Finch who last worked at the station house on the same day the concrete was poured. A broken glass photographic negative that was buried with the victim is the vital clue that leads them to the murderer.