The hero, Grady, is compelling as he pursues a twisted criminal with the help of FBI agent Gary Guhleman (from book 1 of the series, Deadly Alliance). Grady has chemistry with Tori, who works her own case as a sleuth running a food truck. Heroine Tori is a wonderful character as well with plenty of courage and intelligence. They have differences of opinion mostly about Vivienne. Their love scenes are exciting without seeming misplaced or excessive, and their relationship is developed in a way that feels natural and true.
There is also plenty of humor to break up the tension, not only between Tori and Grady but with secondary characters, Finn and Amy Donahue, from Deadly Alliance. Unholy Alliance has danger, suspense, lust, love, revenge, justice and even an adorable old bloodhound, Sherlock.