Who is Vuong Van Luong from The Tears of Autumn and what is their importance?

Vuong Van Luong is a South Vietnamese intelligence agent working for Paul Christopher (whose surname, he thinks, is Crawford), Luong has made enemies with Ngo Dinh Diem and Ngo Dinh Nhu and is facing sure execution when he returns to Saigon. Luong is first seen in Vientiane, Laos, where he has observed and photographed a meeting between his boyhood chum, Do Minh Kha, now a high North Vietnamese official, and a mystery young woman. The South Vietnamese secret police are watching to see if Paul will tip Luong.