THE HISTORICAL LEDGER gives famous spies and traitors a celebrity they rarely sought in their own lives. For Americans, treason and Benedict Arnold are synonymous. When we admire noble patriotism, we think of Nathan Hale, executed by the British as a spy in September 1776, regretting that he had only one life to give for his country. But the most accomplished spy of the American Revolution, Edward Bancroft, was a man whose name is known only to scholars. It took a whole century for knowledge of his espionage to become part of the history of the Revolution.

Bancroft was originally recalled as a minor but patriotic figure in diplomatic history, on the basis of his apparently unpaid service as an unofficial secretary to the American diplomatic mission in Paris. Only the publication in 1889 of Benjamin Franklin Stevens’s great photographic reference work, Facsimiles of Manuscripts in European Archives Relating to America, 1773-1783, demonstrated the key finding: that Edward Bancroft and the mysterious “Dr. Edwards,” who was a prime source of British intelligence, proved to be one and the same person. From April 1777 through the peace negotiations of 1782-1783, Bancroft kept the British government fully informed of the work of the American diplomatic mission in Paris. Throughout the war, King George III and Lord North knew far more about what the American diplomats in Paris were doing than the Continental Congress ever belatedly learned. Yet while Bancroft doubtless worried about his security, neither the Americans nor their French allies ever suspected that he was the source of the leaks that seemed to spring and even gush freely from the Franco-American friendship.

Thomas J. Schaeper’s biography is the first work of scholarship that gives Bancroft’s career the fair and properly inquisitive treatment it deserves. In many ways, this is a model biography, not so much in telling the full story of Bancroft’s life—significant parts of which remain elusive—but in carefully assessing what we do and do not know about his activities. In contrast to the detractors who have described and disparaged Bancroft ever since his treachery was revealed, Schaeper weighs the allegations and the charges against him one by one, and in doing so he repeatedly illustrates how history should properly be written. Schaeper takes no statement about the past for granted. He insists that every claim rest on some documented foundation.

Bancroft was born in January 1744 to a Massachusetts farming family. His father died of a seizure in a pigsty before Edward was two, and a few years later his mother remarried. Edward’s stepfather kept the family shuttling between Massachusetts and Connecticut before opening a tavern in Hartford. Edward must have shown strong intelligence as a youth, because at the age of fifteen he became a student of Silas Deane, a young Yale graduate who later became the first diplomatic commissioner whom the Continental Congress sent to Paris.

In 1760, Bancroft became an apprentice to a Connecticut physician, and began acquiring the distinctive intellectual interests he pursued thereafter. In 1763, as the Seven Years War ended, he skipped out of his apprenticeship and sailed off, first to Barbados, and then to Dutch Guiana on the South American mainland. Here he quickly parlayed his medical learning into employment as a “surgeon” to European plantation owners. By 1766, with his savings in hand, he left his medical tasks behind and began journeying through the surrounding countryside, keenly observing the flora and fauna. A year later he sailed briefly back to Barbados and New England before heading off to London, which became his permanent home until espionage drew him to Paris.