Puzzle for Two by Josh Lanyon

Two can play at this game…

Fledging PI Zachariah Davies’s wealthy and eccentric client, toymaker Alton Beacher, wants to hire an investigator who can pose as his boyfriend while figuring out who is behind the recent attempts on his life. And Zach, struggling to save the business his father built, is just desperate enough to set aside his misgivings and take the job.
But it doesn’t take long to realize all is not as it seems—and given that it all seems pretty weird, that’s saying something. The only person Zach can turn to for help is equally struggling, equally desperate, but a whole lot more experienced rival PI Flint Carey.
Former Marine Flint has been waiting for Zach to throw in the towel and sell whatever’s left of the Davies Detective Agency to him. But when the game, inexperienced accountant-turned-shamus turns to him for help, Flint finds himself unwilling—or maybe unable—to say no.