First published in 1887, the short novel "A Study in Scarlet" introduced the world to the character of Sherlock Holmes. This is the "origin story" of the relationship between Holmes & Watson, telling of their first meeting and first case. If not for the strength of the relationship between Holmes and Watson, and the uniqueness of Holmes as a character, I wonder if the plot alone of this novel would have been enough to begin the massive wave Holmes popularity that has developed over the decades.
The book is infamous for its long (more than a third of the novel) digression about Mormon pilgrims on a wagon train to Utah. This serves as the backstory for the mystery, which is a rather pedestrian case of revenge. The Mormons take in a father and his adopted daughter, who are in danger of dying of thirst in the wilderness. In exchange for rescue, the pair agree to become Mormons, but the father refuses to engage in the practice of polygamy. Upon reaching the age of marriage, the daughter is forced into a Mormon marriage (the father is killed in an escape attempt), although she has fallen in love with a non-Mormon. Her fiancé spends decades tracking down the men involved in the murder and marriage, leading to his killing of them in London, and his eventual capture by Holmes.
Despite the long proportion of time the novel spends in Utah, the strength of Holmes as a character is evident. His observations are impressive and accurate, he is the proper mix of confident and arrogant, he lacks some social graces, and even plays the violin. It is interesting to see how much of the fundamental aspects of Holmes and his world are present in this first novel. His counterparts among the police, the rivals Lestrade & Gregson, both appear. It was nice to see Gregson, as he rarely if ever appears in expansions and adaptations of the Holmes canon. The team of young street urchins that Holmes uses in his work, the "irregulars," also serve an important function in the story.
Because of the odd narrative choice of the extended backstory, it is hard to consider this a great novel, altough it is certainly an important novel. I don't think that I would recommend that Holmes "newbies" start here. There are much better "jumping on" points later in the series.