Katie and Marcos were nice and steamy and I liked the dark side of this story too. Having read this after reading the second book in this series, The Slayer, this book filled in some of the details for Chuito's story. I feel strange talking about another book in this series in this review, but these two books are very closely related. 
 I liked The Viper. Katie and Marcos were a good match for each other and I loved how the people around them all helped to make it happen between them. I love the gangster elements of this story-- I'm never quite sure what to expect. 
 So, a good start to the series.