H. Paul Johnson and Dudley Foster, the pilot of their three-person research submarine are hunting the smallest, most elusive game imaginable, in one of the most hostile environments on the planet. They were on an expedition to test a provocative theory:that there is a vast, clandestine horde of microscopic orgnisms thriving deep below the sea floor in the Earth's crust. Mounting evidence, including newly discovered fossil signs of rock eating microbes living almost a mile beneath the ocean bottom, suggests that this zone is a giant incubator of life.