I quite liked this book, which is by Jon Meacham. Here is the bit best suited to MR:
“She [Sally Hemings] was just beginning to understand the French language well, and in France she was free, while if she returned to Virginia she would be re-enslaved,” said Madison Hemings. “So she refused to return with him.”
It was an extraordinary moment. Fresh from arranging terms with the bankers of Europe over a debt that was threatening the foundation of the French nation, Thomas Jefferson found himself in negotiations with a pregnant enslaved teenager who, in a reversal of fortune hardly likely to be repeated, had the means at hand to free herself.
…So he began making concessions to convince Sally Hemings to come home to Virginia. “To induce her to do so he promised her extraordinary privileges, and made a solemn pledge that her children should be freed at the age of twenty-one years,” Madison Hemings said.
Sally Hemings agreed…
Their father kept the promise he had made to Sally in Paris. “We all became free agreeably to the treaty entered into by our parents before we were born,” Madison Hemings said. It was one of the most important pacts of Jefferson’s life.