A handsome young New York professor comes to Phoenix to research his new book. When he is brutally murdered, police connect him to one of the world's most deadly drug cartels. This shouldn't be a case for historian‑turned‑deputy David Mapstone—except that the victim had been dating David's sister‑in‑law, Robin, and now she's a target too. David's wife, Lindsey, is in Washington with an elite anti-cyber-terror unit and she makes one demand of him: protect Robin. This won't be an easy job, with the city police suspicious of Robin and trying to pressure her. With the sheriff's office in turmoil, David is even more of an outsider. And the gangsters are able to outgun and outspend law enforcement. It doesn't help that David and Lindsey's long‑distance marriage is under strain. But the danger is real and growing. To save Robin, David must leave his stack of historic crimes and plunge into the savage world of smuggling—people, drugs, and guns—in Phoenix. Arizona's "History Shamus" returns inSouth Phoenix Rules. It's the most gripping and personal David Mapstone Mystery yet.