The Eternal Flame?!? If you’ve been following the reveals of the Infinity Stones a.k.a. Marvel’s magic MacGuffins, you know the Tesseract showed up in Avengers (as did Loki’s Scepter, though that’s not outed as a Stone until Age of Ultron), The Aether (the Reality Stone) appeared in Thor: The Dark World, The Orb showed up in Guardians of the Galaxy -- where the Collector finally told the backstory of the stones and gave us a glimpse at the unique colors for each one -- Ultron outed Loki's scepter as the Mind Stone (which the villain used to create Vision) and Doctor Strange (in Doctor Strange) slyly dropped that the Eye of Agamotto necklace was the Time Stone. That leaves one Stone left: The Soul Stone.
Many people assumed that the Soul Stone would be revealed in Thor: Ragnarok -- yours truly among them. It seems to fit so perfectly: the goddess of death Hela wanting a Soul Stone, Thanos wanting to court death in the storyline from the comics, even the acrostic theory -- where the objects hiding each of the stones spell out “THANOS” with the first letter of their noun (T for Tesseract, H, A for Aether, N for Necklace, O for Orb, S for Scepter) -- worked out. The “H,” us smart-asses thought, was for Heimdall, Idris Elba's all-seeing, bridge operator.