In 1748, Scottish noblewoman Lady Jane Douglas gave birth to twin boys in Paris. Although she and one of the boys died in poverty five years later, her surviving son was heir to one of the greatest fortunes in England, and would become one of the most important men in the empire—if his inheritance were secure. But was Archibald Douglas really Lady Jane's son? His mother was fifty at the time of his birth—an incredible circumstance in any century—and if it could be proven that Archibald was adopted, the fortune would pass to another. The Douglas Cause, one of the greatest scandals in English history, a legal case whose twists and turns mesmerized the British public, led the citizens of Edinburgh to riot, and threatened to undermine the very fabric of the empire. Based on six years of research, The Heir of Douglas is the thrilling, definitive account of an astonishing court case, written by a woman who "knows her way about in the eighteenth century" (The New York Times).