)[3] On July 14, 1763, after fleeing his apprenticeship, Bancroft left New England for the sugar-producing slave colonies of Dutch Guiana, where he became a plantation doctor.

Based on observations of experiments already being performed on live eels by Dutch colonists in and around Surinam and Essequibo, Bancroft concluded that American eels and torpedo fish discharged electricity to stun their prey, rather than by an imperceptibly swift mechanical action, as had previously been argued.

The epistolary novel, which follows the life of a plantation owner (with the same surname as his friend and employer), imitates Voltaire's Candide and reflects Bancroft's deistic beliefs, ridiculing passages in the Bible and criticizing Christianity for its "detestable spirit of intolerance and persecution.

In the letter, Deane said they would discuss procuring goods for trading with the Indians, and he enclosed thirty pounds (a generous amount) for travel expenses.

[2] In London, Bancroft sent copies of recent newspapers and pamphlets on current affairs and long letters to Deane to keep the Americans informed about the thinking of the British government and people.

Bancroft arranged to have his dispatches smuggled into France in French diplomatic pouches to avoid having them opened by the London post office.

[16] Though Bancroft had worked for Franklin and Deane, he was unenthusiastic about American independence, and the possibility of a French war against Britain alarmed him.

A couple of days later, on August 14, 1776, Bancroft composed a nine-page report detailing what Deane had been able to accomplish since arriving in France.

Every Tuesday after 9:30 PM, he put the letter in a bottle, tied a string around it, and left it in a hole in a certain box tree in Paris.

[2] Bancroft was "successful but ineffective"; that is, though he gathered a good deal of information, the British were unable to prevent a Franco-American alliance.

In December 1777, John Paul Jones arrived in France, expecting to be given command of the ship Indien being built in Amsterdam.

[a] In the summer of 1777, Arthur Lee charged that Bancroft had met with members of king's privy council; and in April 1778, a sea captain named Musco Livingston told Lee that in London he had seen a letter written by Bancroft that provided details about the French treaty before it had been signed.

)[22] On January 19, 1777, Franklin wrote to Juliana Ritchie, a woman living in a Benedictine convent in Cambrai, that even if he suspected his valet to be a spy, "as he probably is, I think I should not discharge him for that, if in other Respects I lik'd him.

Bancroft responded by publishing in several newspapers an account provided by the ship's captain, which stated that Deane had become suddenly ill and had been unable to say anything comprehensible during the four hours before his death.

[27] In the years since Boyd's articles appeared, his thesis has been largely dismissed as "ungrounded conjectures"; nevertheless, the theory has been widely publicized in a popular American textbook: James West Davidson and Mark Hamilton Lytle, After the Fact: The Art of Historical Detection (Boston: McGraw Hill, 1982 [sixth edition, 2010]).

[28][29] Following the Revolutionary War, Bancroft obtained patents to import black oak into Britain and France to be turned into a yellow dye called quercitron; and he convinced John Paul Jones to invest a large sum in the business.