I don't know that According to Hoyle by Abigail Roux is the most underrated book ever, but I sincerely believe that it is underrated within the genre (M/M) and within Abby's own fandom. :)
Abigail Roux is best known for her Cut & Run series, featuring the adventures of a pair of FBI agents who also become lovers. GREAT books. I love them. There's a whole huge fandom that's been built up around this series and I think that According to Hoyle, which is not part of Cut & Run, suffers and languishes in the afterthoughts of many of Abby's fans.
It's a historical, western in flavour. The characters are full and flawed and very, very human. The story focuses on 4 of them, two US Marshals and two outlaws. Eli and William are the marshals and it's their interaction with the outlaws they're transporting, Dusty and Cage, that enables them to face their deep feelings for each other. And it's a mystery and an adventure and a love story and just so much fun! And Cage? The man is mute. Can't talk. And the way Abby is able to bring him alive is so very amazing. He's fascinating and I want... no NEED to know more about him
I understand the love for Ty and Zane from Cut & Run and the wish for more and more of their adventures and the adventures of their Team Sidewinder buddies, but I keep my fingers crossed for another book about the great characters in According to Hoyle and try not to think that they may have gotten lost beneath the hype of C&R.