Across a Billion Years by Robert Silverberg

Graduate student Tom Rice is thrilled to embark on his first deep-space archeological expedition. He is part of a team from Earth, venturing out in search of artifacts from a civilization that ruled the universe many millennia ago. Called the High Ones, the members of this long-gone society left tantalizing clues about their history and culture scattered throughout space. One such clue, a "message cube" containing footage of the ancient ones, is more interesting than all of the others combined. It seems to indicate that the High Ones aren't extinct after all--and just like that, Tom Rice's archeological mission has become an intergalactic manhunt, one filled with ever-increasing danger that will send the explorers hurtling headlong into the greatest adventure--and peril--of their lives.