Charles Sheffield

Even though he has conquered the warlike Zardalu, Hans Rebka is faced with yet another challenge when a mysterious force begins destroying stellar systems, forcing Rebka and his band of humans and aliens to save the galaxy.

The Zardalu were the greatest menace in the galaxy, enslaving many races, exterminating others. It was fortunate that they had become extinct aeons before humans ventured into space. But then Hans Rebka, Darya Lang, and a motley group of human and other beings were investigating the gigantic and inexplicable artifacts left behind by the mysterious vanished race known only as the Builders when they came across a horde of Zardalu who have been in...