The murder of two members of the Capitol Cleaning Service might've been just another homicide investigation if one of them hadn't been romantically involved with a married senator from Arizona.

Lt. Sam Holland and her team are plunged into another complex case that at first seems routine. But as Sam tugs on the threads of the investigation she uncovers a deep, dark Washington secret that threatens the careers of some of the government's highest-ranking officials. Racing to catch a killer before he can strike again, Sam and her fiancé, U.S. Senator Nick Cappuano, attempt to plan a wedding while her colleague Detective Tommy "Gonzo" Gonzales faces life-changing news.