A Time magazine and New York Times Best Book of the Year Charles Mason (1728–1786) and Jeremiah Dixon (1733–1779) were the British surveyors best remembered for running the boundary between Pennsylvania and Maryland that we know today as the Mason-Dixon Line. Here is their story as reimagined by Thomas Pynchon, featuring Native Americans and frontier folk, ripped bodices, naval warfare, conspiracies erotic and political, major caffeine abuse. Unreflectively entangled in crimes of demarcation, Mason and Dixon take us along on a grand tour of the Enlightenment’s dark hemisphere, from their first journey together to the Cape of Good Hope, to pre-Revolutionary America and back to England, into the shadowy yet redemptive turns of their later lives, through incongruities in conscience, parallaxes of personality, tales of questionable altitude told and intimated by voices clamoring not to be lost. Along the way they encounter a plentiful cast of characters, including Benjamin Franklin, George Washington, and Samuel Johnson, as well as a Chinese feng shui master, a Swedish irredentist, a talking dog, and a robot duck. The quarrelsome, daring, mismatched pair—Mason as melancholy and Gothic as Dixon is cheerful and pre-Romantic—pursues a linear narrative of irregular lives, observing, and managing to participate in the many occasions of madness presented them by the Age of Reason.