Heechee Rendezvous

Once the galaxy was ruled by Heechee, benevolent aliens with almost godlike powers. 500,000 years ago, they encountered an even more powerful race. To prevent their own destruction, the Heechee fled to the relative safety of a black hole, leaving behind only traces of their civilization.
Millennia passed. Humankind discovered the Heechee legacy--in particular an asteroid stocked with autonavigating spacecraft. In GATEWAY the impoverished Robinette Broadhead won a lottery ticket to the asteroid, rode a Heechee ship into interstellar space & returned to Earth a conscience-stricken millionaire. Then in BEYOND THE BLUE EVENT HORIZON, Broadhead financed & eventually led the expedition which unlocked many secrets of Heechee technology.
Now, in HEECHEE RENDEZVOUS, Robinette Broadhead is forced once more to make a perilous voyage into space--where the Heechee are waiting. And this time the future of our species is at stake.