The Collectors

An omnibus edition of the Titan, Rhea, and Tharsis stories

A manned mission to look for signs of life in the methane sea on Titan discovers much more than expected below the surface of the small moon. After returning from the mission, one of the crew tells her story but nobody believes her.
Five years later mining and science teams are sent to Rhea, another of Saturn's moons. The miners bore a hole down into a massive underground cavern. When the science team arrives later they find a very unexpected and disturbing link to the Titan mission. Events on Earth change the focus of space exploration to establishing bases on Mars.
Fifty years later a small base has been established just south of the Tharsis Mons mountain range on Mars. A chance discovery by a geological survey team leads to a strange connection to the space stories they all knew from the old Titan and Rhea missions.