Night of the Assassin, by Russell Blake

This novel is a prequel to King of Swords, providing the back story for "El Rey" (the assassin).   It was entertaining and interesting.   Although it feels odd to root for the bad guy, since El Rey's targets are exclusively drug kingpins in Mexico, being sympathetic to the killer was easy.

This isn't great literature, but if you can get it at a discounted Kindle edition price, it is worth the read.