Unlike what the title says, this isn't Mistborn the Final Empire (the first MB book). Its Mistborn: Secret History. I would strongly recommend reading all three of the first MB books (Final Empire, Well of Ascension and Hero of the Ages) before reading this book. It spoils the endings of all 3 books. Secret History begins towards the end of Final Empire, and continues the story of Kelsier. It takes place 'in the background' of the first trilogy, and it explains a lot of things that don't get explained throughout the series. It also gives a better glimpse of the original 'gods' of Scadriel, as well as showing bits of other worlds and realms in the cosmere. I read SH after reading the 6th Mistborn book, and it even provided a lot of context to what was happening in that book. Secret History is described as a 'one off', but after reading Bands Of Mourning, I would have to say its a must-read if you want the full story of the series. It should technically be book 3.5, being read before Alloy of Law but after the main trilogy.