This book begins the sequel to Faithful Wife's Fall From Grace that ran 8 books (i.e, Books 1-8). Those books told the story of a husband (Mike) who fantasized about his wife (Jen) with other men. That fantasy became a reality. While intensely thrilling for both of them, things spiraled out of control.
There was a lot of emotional angst and heartbreak in those 8 books. By the end, though, Mike and Jen were still husband and wife.
Given how close they had come to losing each other, Mike and Jen became sexually and emotionally exclusive to each other again, and looked forward to a normal monogamous marriage that didn't include other people (other men) in Jen's sex life.
In this sequel, Mike and Jen discover that fantasies can't be buried forever. Especially when, for Mike (a cuckold) and Jen (a hot wife), their fantasies are so ingrained, so powerful, they're like sexual orientations.