The farther shore - Christie Golden

When the long-lost Starship Voyager returned home to Earth, did Kathryn Janeway and her crew unwittingly bring with them a deadly Borg infection from the heart of the Delta Quadrant? Many in Starfleet think so, and Seven of Nine finds herself the prime suspect as the carrier of the plague.
Now, following the events of Homecoming, Admiral Janeway must reunite her crew in a desperate attempt to discover the source of the contagion -- and save the people of Earth from total assimilation into a voracious Borg collective.