It's hard not to be of two more or less uneasy minds about this ambitious book. O'Brien (If I Die In A War Zone, Northern Lights) has come directly to his subject--Vietnam--with great formal care and deep knowledge, and yet at least half the time it feels as if he's traveling in someone else's boots. In a fugue of fantasy chapters interspersed with astringently realistic flashbacks, Specialist Fourth Class Paul Berlin endures the life of a foot-soldier in Quang Ngai province; when a grunt named Cacciato--"dumb as a bullet"--one day picks up and sets off through the jungle, destination Paris, Berlin's patrol is sent after him. Fantasy takes over as, through Laos, India, Iran, Greece, and finally Paris, a dream of "possibility" and peace develops that could not be in greater contrast to the hell (in flashbacks) of normal war: the fragging of a by-the-book lieutenant, a medic feeding a dying soldier M&Ms and calling them "pills," desperate basketball games in the jungle. The revulsion, pity, and sheer documentary vividness O'Brien can draw from his real-Vietnam material is truly remarkable. But the fantasy journey and the Cacciato metaphor lack parallel strength: "The real issue was the power of the will to defeat fear. . . . Somehow working his way into that secret chamber of the human heart, where, in tangles, lay the circuitry for all that was possible, the full range of what a man might be." Such fustian/imitation-Hemingway tendencies rub up against balloony characters like a young Vietnamese refugee girl who accompanies the Quixote-like patrol on its mission to Paris and who seems more like an obligation to story than a deeply felt personality. "Where was the fulcrum? Where did it tilt from fact to imagination? How far had Cacciato led them?" Paul Berlin wonders--and so do we as we follow O'Brien through what's too often a large shell that unfairly shadows writing and intelligence of the highest order and honesty.