A story of alchemy in Bohemian Paris, where two scientific outcasts discovered a fundamental distinction between natural and synthetic chemicals that inaugurated an enduring scientific mystery. For centuries, scientists believed that living matter possessed a special quality—a spirit or essence—that differentiated it from nonliving matter. But by the nineteenth century, the scientific consensus was that the building blocks of one were identical to the building blocks of the other. Elixir tells the story of two young chemists who were not convinced, and how their work rewrote the boundary between life and nonlife. In the 1830s, Édouard Laugier and Auguste Laurent were working in Laugier Père et Fils, the oldest perfume house in Paris. By day they prepared the perfumery’s revitalizing elixirs and rejuvenating eaux, drawing on alchemical traditions that equated a plant’s vitality with its aroma. In their spare time they hunted the vital force that promised to reveal the secret to life itself. Their ideas, roundly condemned by established chemists, led to the discovery of structural differences between naturally occurring molecules and their synthetic counterparts, even when the molecules were chemically identical. Scientists still can’t explain this anomaly, but it may point to critical insights concerning the origins of life on Earth. Rich in sparks and smells, brimming with eccentric characters, experimental daring, and the romance of the Bohemian salon, Elixir is a fascinating cultural and scientific history.