William Gascoigne (c.1612-44) was the inventor of the telescopic sight and micrometer (instruments crucial to the advance of astronomy). His name is now known to historians of science around the world. For some considerable time after his tragic death at the age of 32 in the English Civil War, however, it seemed as if his achievements would be consigned to oblivion. Most of his papers were lost and even the few that survived have largely disappeared. This is the story of how his work was rescued. Into this story is woven an account of the state of astronomy and optics during Gascoigne’s lifetime, so that the reader can appreciate the significance of his discoveries.