The Golden Torc by Julian May

In a world where time travel and psychic abilities intertwine, a group of modern-day humans ventures into the distant past, joining the ranks of the alien-influenced Pliocene Epoch. Here, they encounter a society dominated by the Tanu and Firvulag, two powerful alien races with their own agendas. As the newcomers navigate this complex and dangerous world, they must grapple with the allure of the mind-enhancing golden torcs and the intricate politics of the alien factions. Amidst the struggle for power and survival, alliances are forged, secrets are unveiled, and the boundaries of human potential are tested in a tale of adventure and intrigue.

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