Perfectly Dead by Michael A. Stackpole

Perfectly Dead is the second in the Homeland Security Services series. HSS agents Miracle Dunn and Abraham Fyn are sent to Phoenix to investigate the occult murder of Connor Moran. Moran—a failed science fiction author—hadn’t an enemy in the world, and evidence at the site fits a frame firmly around a friend of his. And at the same time Moran was being murdered, the notes and manuscript for his new novel are stolen from his apartment. Fyn and Dunn rely on world-famous occultist Merlin Bloodstone to sort the mystery out, and the conspiracy they uncover reaches as far as the highest offices in the land.

The Homeland Security Services novels are set in an alternate history where the first attack on the Twin Towers successfully dropped them into the city, killing tens of thousands. Three years later, terrorists successfully attacked the Democratic National Convention in Chicago, wiping out the political leadership of the nation’s left wing and propelling Speaker of the House, Newt Gingrich, into the White House. The Patriot Amendment to the Constitution redefined what it is to be an American citizen.