"The Immortality Key: The Secret History of the Religion with No Name" is a book by Brian C. Muraresku that explores the possible connection between ancient Greek mystery religions and early Christianity through the use of psychoactive substances, particularly psychedelics. Muraresku delves into archaeological evidence, historical texts, and personal experiences to propose that psychedelics may have played a significant role in the religious practices of ancient civilizations, including the Eleusinian Mysteries in Greece. He suggests that these substances could have been used to induce spiritual experiences and visions, leading to the development of religious beliefs and rituals that influenced the origins of Christianity. Overall, the book offers a provocative exploration of the intersection between religion, history, and altered states of consciousness.