Heechee Rendezvous — Frederik Pohl

Once the galaxy was ruled by the Heechee benevolent a lens with almost godlike powers. But five hundred thousand years ago, they encountered an even more powerful race, and 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 and Mankind 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 and returned to Earth a conscience-stricken millionaire. Then in Beyond the Blue Event Horizon, Broadhead financed and, 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 Man is at stake...