The Enemy Within

One of Kristine Kathryn Rusch's most acclaimed short stories becomes one of her most original novels. February, 1964: Two men die in a squalid alley in a bad neighborhood.  New York Homicide Detective Seamus O'Reilly receives the shock of his life when he looks at the men's identification: J. Edgar Hoover, the famous, tyrannical director of the FBI, and his number one assistant, Clyde Tolson. O'Reilly teams up with FBI agent Frank Bryce to solve the second high-level assassination in only three months.
Because in November of the previous year, someone assassinated President John F. Kennedy. The cop and the FBI agent must determine if the same shadowy organization committed all three murders. To do so, they must act quickly before some of the nation's most powerful men-from Kennedy's brother, Attorney General Robert F. Kennedy, to the President of the United States, Lyndon Baines Johnson-do something rash to keep Hoover's secrets from ever becoming public.
In our world, Hoover kept his secrets until long after his death. In Seamus O'Reilly's world, Hoover's secrets get him killed. The Enemy Within offers alternate history so plausible that only Kristine Kathryn Rusch could have written it. Winner of the 2014 Sidewise Award for Best Long Form Alternate History."A dark, yet fascinating tale, The Enemy Within gives readers an intriguing look at what could have happened in 1964 New York."-RT Book Reviews"[Enemy Within] is a blend of mystery, political thriller, and alternate history.
It was a compelling read I had trouble putting down.