This one is one of Sherlock’s failures, on two levels.
First, despite that he did find out about the history of the murders through his deduction and research, Sherlock and Waston were utterly powerless in preventing the murder of his client, and did not catch the murderer as they always did. In stead, it was the god (or the author, to be more precise) who served justice by sinking the ship in the Atlantic.
On the other hand, which is more important, the writing of the story is a failure. Especially when compared with A Study in Scarlet, which share a similar background where some bad deeds committed by some fanatic cults in the New World spilled back to the Old England (Doyle had a constant interests of commenting on the repression and violence committed by colonialism and exploration), this story lacks any kind of devotion or seriousness from the author. The plot was clumsy and the writing was sloppy. The clues were bizarre, and in this case the KKK appeared to be more organized, secretive, and sinister than the Mormons. But the story failed to generate any of the darkness and suspense a Sherlock story normally has. It reads more like a tabloid news article rather than a engaging story.