Abduction
Robin Cook
 A team of researchers in a remote region of the Atlantic become trapped inside an ancient undersea volcano when their submersible is inexplicably drawn in. They discover a technologically advanced world of genetically engineered, physically near-perfect humans living comfortably in an enclosed city within the Mohorovičić discontinuity. The researchers are told that their Moho-dwelling cousins evolved many millions of years prior to current humans and became very technologically advanced. Millions of years ago, these "first generation" humans discovered that Earth was about to be bombarded with hordes of meteors, effectively sterilizing the surface of the planet. Unable to find a suitable extrasolar planet to move to in time, the first generation humans decided to instead move into the Mohorovičić discontinuity, shielding themselves from extinction. The Moho-dwellers watched over the centuries as the second-generation humans evolved and developed, and reveal that they abducted these researchers to determine if the researchers had been searching for them. The researchers reveal that nobody on the surface has ever thought there were civilizations living under the Earth's crust, and that they were doing geologic exploration and research instead. Fearing for their own safety and the discovery of their civilization, the Moho-dwellers feel they cannot allow their abductees to return to the surface. The research team manages to recover its submersible and mounts an attempt to return to the surface. However, at the last moment they encounter a large Moho craft and emerge to the ocean's surface in the late 18th century. The group abruptly discovers that the craft was actually some sort of advanced Moho time machine and/or spacecraft that sent them 200 years into the past to prevent them from alerting the surface world to the presence of the Moho-dwellers.