Honestly, I'm quite surprised that this novel doesn't seem to be rated that highly by readers. I personally think that it's a masterpiece. Conan Doyle uses a similar technique to A Study In Scarlet, going back to provide the background to the main case, and to be honest, I think that the flashback part might be my favourite segment of any Sherlock story. I know, it's a pretty bold take, but that's just how I feel about it. The atmosphere of the 'Valley of Fear' is true to its name, and the tale of McMurdo is riveting. And of course, the final twist. What a mic drop moment, man.