The Mote in God’s Eye (Moties, #1)

In the year 3016, the Second Empire of Man spans hundreds of star systems, thanks to the faster-than-light Alderson Drive. No other intelligent beings have ever been encountered, not until a light sail probe enters a human system carrying a dead alien. The probe is traced to the Mote, an isolated star in a thick dust cloud, and an expedition is dispatched. In the Mote the humans find an ancient civilization–at least one million years old–that has always been bottled up in their cloistered solar system for lack of a star drive. The Moties are welcoming and kind, yet rather evasive about certain aspects of their society. It seems the Moties have a dark problem, one they’ve been unable to solve in over a million years.