The Prometheus Project

Bob Devaney was a Special Forces soldier in the early 1960s - until a certain traumatic event, which he refused to discuss even with his superiors, caused him to leave the Army and set up his own security and investigative agency, an agency whose one employee was himself.
Hired by a secret government agency to do undercover work, he was escorting a mysterious woman named Novak to the White House when they were ambushed by gunmen. Novak used a device that worked like an invisibility field to make an impossible escape - and then knocked Devaney out with some kind of ray gun. When he woke up, he realized Novak was about to kill him for knowing too much - but suddenly she received a message: Devaney was to be recruited for something called the Prometheus Project.
The Project turned out to be the largest disinformation operation in history, targeted at the aliens who ruled the galaxy. A man named Inconnu had arrived in a damaged but highly advanced craft in the 1940s with the information that he had escaped from a group of humans whom aliens had been studying, and it turned out that unless the Earth could convince the aliens that the planet had a unified government, and was armed with technology comparable to that of the galactic rulers, the Earth would be exploited as a primitive protectorate.
So far the hoax was working - and the technology which Inconnu had brought with him helped - but someone in the Project was selling secrets to an interstellar mafia called the Tonkuztra about the real state of affairs on Earth. And Devaney knew that Chloe Bryant, the woman he had fallen in love with, was being set up to take a fall for the real traitor, who was about to embark on a treason whose consequences could jeopardize the very Universe.