While the French Army in Indo-China is grappling with the Vietminh, back in Saigon a young and high-minded American named Pyle begins to channel economic aid to a ''Third Force.''

Caught between French colonialists and the Vietminh, Fowler, the narrator and seasoned foreign correspondent, observes: ''I never knew a man who had better motives for all the trouble he caused.'' As young Pyle's policies blunder on into bloodshed, the older man finds it impossible to stand aside as an observer. But Fowler's motives for intervening are suspect, both to the police and to himself: for Pyle has robbed him of his Vietnamese mistress.

''No serious writer of this century has more thoroughly invaded and shaped the public imagination than Graham Greene.'' (Time)