The Middle-Man, Olen Steinhauer

July 4th is the start of a revolution, a left wing terrorist group called Massive Brigades has taken a pick axe to democracy. To try and apprehend the leaders, FBI special agent Rachel Proux will have to go further back. Her investigation leads her to a group of cafe radicals who inexplicably turned to violence and then self-destructed.
The FBI has a deep cover agent embedded in Massive Brigades and he and Rachel are going to have to trust each other to survive.