Heechee Rendezvous

The third novel in Frederik Pohl's 'Heechee Saga', continuing the story of mankind's discovery of, and search for, an ancient space-faring civilization that had risen and then disappeared before the time intelligent life developed on earth. Preceded by "Gateway" and "Beyond the Blue Event Horizon". Followed by "The Annals of the Heechee" and "The Boy Who Would Live Forever: A Novel of Gateway"