<P>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 re-imagined by Thomas Pynchon featuring Native Americans and frontier folk ripped bodices naval warfare conspiracies erotic and political and major caffeine abuse. We follow the mismatched pair--one rollicking the other depressive; one Gothic the other pre-Romantic--from their first journey together to the Cape of Good Hope to pre-Revolutionary America and back through the strange yet redemptive turns of fortune in their later lives on a grand tour of the Enlightenment's dark hemisphere as they observe and participate in the many opportunities for insanity presented them by the Age of Reason.</P>