MISSION IN TORMENT By John Meek-I'm. 318 pages. Doubleday. $4.95.
The overthrow and subsequent murder of President Ngo Dinh Diem in November 1963 opened a political Pandora's box in Saigon. Since that angry day, the government has changed hands seven times; the war against the Communist Viet Cong has grown even tougher; the U.S. has been forced to escalate the conflict by bombing North Viet Nam and nearly doubling its own forces in the south. Most important, Diem's fall brought to an end nearly a decade of political stability in Viet Nam. Was Diem's downfall inevitable or even imperative, the product...