The Fifth Assassin by Brad Meltzer

Description

From John Wilkes Booth to Lee Harvey Oswald, there have been fourteen assassination attempts on the President of the United States.
Four have been successful.
But now, Beecher White — the hero of the #1 bestseller The Inner Circle — discovers a killer in Washington, DC who's meticulously recreating the crimes of the world's most famous assassins:
John Wilkes Booth.
Charles Guiteau.
Leon Czolgosz.
Lee Harvey Oswald.
But what's scariest of all is what all four assassins have in common.
Historians have branded them as four lone wolves. But what if they were wrong?
Beecher is about to find out the truth: that over the course of a hundred years, all four assassins were secretly working together. What was their purpose? Who do they really work for? And why are they planning to killing the President today? Beecher's about to find out. And most terrifying, he's about to come face-to-face with the fifth assassin.