Jack McDevitt 
Omega (Academy – Book 4) 

‘No one writing today is better than Mc Devitt at combining galaxy-spanning adventure with the genuine novel of ideas’ Washington Post Book World A civilization-destroying Omega cloud has switched direction, heading straight for a previously unexplored planetary system – and its alien society. A handful of brave humans must try to save an entire world … without revealing their existence.’Mc Devitt handles the back story so adroitly that readers unfamiliar with earlier volumes in this series should have no trouble following the action’ New York Times Book Review