I really don’t think I read this one when it came out (in 1974). The novel’s hero, Paul Christopher, is the same one as in The Miernik Dossier. In this book he’s a agent living in Rome and meeting his case officer in Paris. While in the Congo in November of 1963, he hears about the Kennedy assassination from a Belgian priest at the airport in Léopoldville (later Kinshasa). Coincidentally an agent of his gives him intriguing information that causes him to try to connect the Kennedy assassination with the deaths of Diem and Nhu in what he supposed (though it was not generally known at the time) was an American-sponsored coup in Saigon. Christopher is convinced that he has enough contacts to prove that the instigators of the assassination were in Vietnam. His superiors in the US government, though, find his theory preposterous and refuse to sanction his operation. Christopher quits “the outfit” [CIA] and works on his own, though he gets unofficial help from former colleagues. Traveling to Africa, Asia, North American and Europe, Christopher tracks down the plotters and convinces them (by logic or force) to give him the proof. He deals with an American gangster in Calabria, the head of the Ngo family (to which Diem and Nhu belonged) and his daughter, a North Vietnamese agent, a defecting Russian agent, a Cuban freedom fighter in the Congo and others. He convinces those who help him to keep key people alive (when the collaborators would prefer otherwise) so that proof can be verified later. The Vietnamese family, who want the US out of Vietnam, cooperates, when it does, because Christopher tells them the American people would be so horrified at the truth that they’d never authorize another cent being spent to help Vietnam. There’s a side issue when Christopher finds the Vietnamese family consolidating heroine production which he interprets as a strategy to hook the millions of American service men who seem destined to arrive soon. (Remember, in 1963, the Vietnam war was not full blown and the American presence was primarily relatively small numbers of military advisors.)
The details of the plot are fascinating and, I must say, believable. When Christopher presents his case to representatives of the Johnson administration, however, it’s canned and the evidence destroyed. They don’t want the president to know and either stop the military intervention or feel conflicted about not doing so because of what he knows.