Charlie is a young woman who is a Speleologist and explores caves for a living. She is from Australia, and she is going to work with a scientist named Dr. Fosberg who helped her discover a new cave system. Charlie wonders how Dr. Fosberg knew the cave was there, because it had been buried and sealed up by someone. The cave is also on Aboriginal land. 
Charlie and Dr. Fosberg get geared up and descend further down into the cave. Dr. Fosberg reveals he is curious about the cave because his research shows that earthquakes center at the cave, although they start at the north and south coasts and then converge there. It happens in nine-year intervals. Fosberg and Charlie get to what looks like a dead end, but Charlie realizes that it is not. She refuses to use her tools to open a sealed wall until Dr. Fosberg tells her the whole story. Dr. Fosberg reveals that he believes the earth is hollow, because there is too much evidence of the Underworld from different cultures. There are references in norse mythology to three stones in a point with caves separating them, known as the "Apex of Providence." 
Charlie is curious, so she continues to help Dr. Fosberg. They whittle through the sealed wall and enter into another passage. They see a figure at the edge of the light, who is revealed to be a dead, aged body sitting cross-legged. A few days later, more of the team joins them. Charlie is by herself, exploring father down the cave and radioing to the team above. She insists on going down farther, and they send supplies on a rope beside her. She starts descending, and there is mist everywhere. Her rope slips, and she begins descending very quickly until she kicks her legs out and slams to a stop.
Charlie is in a pool of water a few inches deep. The bottom is black. She begins to sink in the bottom, and she must keep wrenching her feet free. The rope is no longer at her feet, but above her head, and it is too slippery for her to grab. Her supplies are buried, and she sits in the water and moves every few minutes to prevent sinking. She falls asleep, and wakes up sunk to her hips. Suddenly, she feels the rope above her and grabs it. As she climbs upwards, the seabed shakes. The spot she freed herself from is not sealing; instead, it is twisting down and liquid is bubbling from it. Waves form and crash up towards her, and she is fully submerged by one. Fosberg yanks her up. A deep shaking comes from below, and Fosberg reveals that the others ran off but he did not want to leave her. Two things sweep across the sea from the north and south and collide with a crack, and an eye opens between them.
Later, earthquakes have taken over the earth and hundreds of millions of people have died along the world's coasts. Fosberg and Charlie are near the Andes, waiting to see what happens. Fosberg believes that they are in Ragnarok. The ground shakes over and over again, and in the distance, they see the Rainbow Serpent, a creature given different names in many different cultures. They see the Serpent's eye and its following body off in the distance as part of a continent collapses.