A civilization-destroying omega cloud has switched direction, heading straight for a previously unexplored planetary system--and its alien society. And suddenly, a handful of brave humans must try to save an entire world--without revealing their existence.

Accolades:

John W Campbell Award Winner 2004.

Review:

From the New York Times:
McDevitt takes his time moving all the players in this drama into position. He handles the back story so adroitly that readers unfamiliar with earlier volumes in this series should have no trouble following the action. Finally, he provides a satisfying answer to the mystery of the omegas that is appropriately cosmic without straining credulity. — Gerald Jonas