This is a masterful book. Schaeper has done what far too many of his predecessors haven't and actually taken the time to look at the documentary evidence and its context(s). By doing so he's able to offer a much more balanced look at Bancroft's role as a British agent within the American mission in France during the Revolution, gauging the impact of Bancroft's efforts in a considered way. He painstakingly rebuts many of the more outrageous claims that have been made about Bancroft's spy career (by Julian Boyd among others), and is able to offer a much more evenhanded and accurate treatment of Bancroft's efforts within the larger British intelligence operation (such as it was).
While the re-evaluation of Bancroft's motivations and impact would be more than enough, Schaeper also widens the view and takes in Bancroft's entire career, as an entrepreneur (who knew that he was involved with the dye industry?), an author (of not only an important natural history of Guiana but also a 1770 novel, The History of Charles Wentworth), and as the widowed father of several young children. Schaeper provides much-needed perspective by putting Bancroft's spying period into context as a reasonably short episode in his long life.
Offering a close and cautious reading of the available sources, and by carefully noting the limits of the documents that have come down to us, Schaeper has given us a book that is historical scholarship at its best. Highly recommended.