The Detective (Sherlock Holmes/Moriarty?)

"A Study in Emerald" follows a detective as he attempts to solve the mystery of who killed one of the Old Ones, a member of the German Royal Family. The detective is clever and extremely observant. He can deduct things about people and events by simple things such as appearance, mannerisms and other small clues. He has very good forensic investigation skills. He is driven by rationality and logic, and even approaches supernatural people and events in the same calm, detached way. He is a master of disguise, using various costumes and disguises to infiltrate places and gain information. He solves the mystery very quickly and easily.

There are several red herrings in the story that suggest that the detective is Sherlock Holmes. The reader is led to assume this at the beginning of the story, which sees the detective living in Baker Street...