This is spin off from Rivera's Her Russian Protector series and while you don't have to read those books to enjoy this one I'd recommend it because there is quite a bit of character crossover.
This has one of my favourite tropes, guy falling for his best friend's sibling, and it's always a winner for me. Kelly's family owns a gym/training facility that's in jeopardy because his father has a gambling addiction and now owes money to loan sharks and the mob.
In order to save the gym and their father Kelly agrees to do an underground fight tournament for the mob. He's a former marine and his brothers are also ex-military but they're still recovering from injuries. Add into the mix, Kelly is trying to protect Beatrice, his best friend Jeb's younger sister, from a stalker.
I enjoy Rivera's writing. This is more erotica and she does a great job with the sex scenes but as a result some of the plot suffers. The stalker storyline is pretty transparent, although the Jeb twist did surprise me. I would have enjoyed more details about the tournament but it was glossed over. Still I found what we did get with the training and the brief fight mentions very interesting.
There is a TSTL moment by Kelly and Bee's bodyguards which had me shaking my head at how easily manipulated they were by the bad guy. I like the Connollys. I'm looking forward to Jack's story and especially Finn's because I'm hoping it will be an M/M, I have my suspicions! :D
A good erotic read. Heavy on the sex and light on plot but with strong, interesting characters that have all very distinct personalities. Not quite a standalone but you're not inundated with other characters to the point where you're swimming in confusion.