A Letter in Scarlet is a published Sherlock Holmes story that is accepted as taking place first in canon timeline. It introduces Watson and explains how he comes about to live with Holmes. The mystery revolves around the brutal death of two people. Sherlock Holmes discovers the man who does it. Now, there is a huge disconnect in the story because Doyle spends about 100 pages on Sherlock Holmes figuring out who committed the crime, and then, he spends 100 pages describing the villain-- one who everyone can sympathize with.
The villain is this ranger/cowboy who meets this woman he falls in love with. The woman is the adopted daughter of a hunter who settles down in Mormon territory but doesn't follow the Mormon creed. The daughter becomes beautiful so suitors begin to make their desire for the girl known; except, these suitors already have three or four wives and the father does not approve. So the mormons begin to terrorize the family until the ranger steps in and secretly provides for an escape into the mountains. He is out gathering firewood when the father is killed and the girl is seized by the mormons. By the time he makes his way back to the Mormon city, the girl is dead from fatigue/broken heart/what have you.
Well, the two suitors flee to England because the ranger has sworn to kill them. He manages to kill them, but Sherlock Holmes is able to capture him. He tells them the story of what happened and why it happened, and the two detectives and the agent from Scotland Yard feel sympathy, but still, he must suffer for his crime. However, the ranger admits that he will probably be dead by the morrow because there is something wrong with HIS heart. And so it happens that Sherlock Holmes' first published victory is all but bittersweet.