This is a Spenser novel. Back in Boston. Back with Hawk and with the lovely Susan. You either love Spenser, his compatriots and all his baggage, or you do not. I do. He is one of a kind - give Spenser a chance; you might grow to love him too (warts and all).
"When Marlene Rowley hires Spenser to follow her cheating husband, Spenser finds not only a two-timing spouse, but another detective hired to shadow the wayward Marlene. Not the most trusting couple in town--but, as in Spenser's about to learn, certainly one of the most dangerous..." worldcat.org
I enjoyed this novel as Spencer and the detective for the other spouse share information on each of their assignments, without any conflict of interest.