A writer on varied subjects (Doctors on Horseback and American Painting: First Flower of our Wilderness) turns to a brisk and trenchant biography of Benedict Arnold. As a picture of the betrayer, and the two other single personalities that had the most prominent bearing on his life- John Andre and Peggy Shippen- it concentrates more on the externals of his career and on the psychological reasons that made Arnold the troubled man he was in the first place. Traditionally, here is the ambitious and brilliant young soldier who rose swiftly from his enlistment to the command that took him to Quebec. Failing there and later at Ticonderoga, the seeds were sown. Others were appointed over him, and, in spite of a later victory against Tryon in Connecticut, Arnold never lost his grudges against the American command. The rest-his troubles with the civil authorities in Philadelphia, marriage to the childish, Tory, Peggy Shippen, gradually firmer dealings with Andre and the betrayal of his command at West Point- is history. A sharply woven, colorful study, marked by assiduous research that uncovers new material on Andre, but without the deep penetration that could have made it a more permanent contribution.