Starbound (Marsbound #2)

Carmen Dula and her husband spent six years travelling to the distant home of the powerful race known as "The Others," in the hopes of forging a truce. But by the time Carmen returns to Earth, fifty years have passed-and the Earthlings have built a flotilla of warships to defend Earth against The Others.

But The Others have more power than anyone could imagine-and they will brook no insolence from the upstart human race.