Darkness

Lieutenant Jack Falco woke up, said goodbye to his wife and daughter, three hours later, his family and half the world's population was dead. When he couldn't put a bullet in his head, Falco did the next best thing, took a commission as captain and left for humanities furthest boundary, Station Pluto.
Five years in a scout-class boat refitted for the long haul, and Falco escapes the horrors of earth only to find something worse waiting in the vast Oort Cloud, an ancient civilization with a history of violent expansion and humanity has unwittingly entered their territory.