The main idea of the story A Study in Emerald is one of mystery, horror and suspense. It tells the tale of an unnamed detective who has been hired to investigate a strange murder case with seemingly supernatural elements. The victim, Sir Charles Baskerville, was found dead on his estate in Devonshire with no visible wounds or signs of struggle; yet all around him were mysterious symbols and evidence that something far more sinister than mere foul play had occurred. In trying to solve this bizarre crime, our hero soon finds himself embroiled in a centuries-old battle between two powerful forces: the Elder Gods and their minions against those loyal to Cthulhu and other Great Old Ones. Through twists and turns that take him from London's foggy streets to Prague's eerie catacombs, our detective must use every clue he can find – including clues left by Sherlock Holmes himself – if he hopes to unravel the truth behind Sir Charles' death before it's too late...