Mother Earth is crying. Yellowstone is dying. New troubles stack up like cordwood for Chief Ranger Glenn Merrill, as earth tremors and an imminent supervolca threaten Yellowstone's existence. After a series of gruesome deaths claims animals, tourists and a ranger, it is clear that something has gone very wrong at the nation's oldest national park. But putting an end to the mysterious deaths is more than just the chief ranger's job - it may be his end. Obsidian Tears plunges Glenn, his Shoshone friend, an aggressive young seismologist and an Arapaho healer into a world of Indian mysticism. Will man and nature join forces, or risk losing all humanity to an ancient evil?