A groundbreaking dive into the role psychedelics have played in the origins of Western civilization, and the real-life quest for the Holy Grail that could shake the Church to its foundations. The most influential religious historian of the 20th century, Huston Smith, once referred to it as the "best-kept secret" in history. Did the Ancient Greeks use drugs to find God? And did the earliest Christians inherit the same, secret tradition? A profound knowledge of visionary plants, herbs and fungi passed from one generation to the next, ever since the Stone Age?