Star Trek: Section 31, book 03 : Shadow
Dean Wesley Smith et Kristine Kathryn Rusch2001

They are the self-appointed protectors of the Federation. Amoral, shrouded in secrecy, answerable to no one, Section 31 is the mysterious covert operations division of Starfleet, a rogue shadow group committed to safeguarding the Federation at any cost.

Someone or something is trying to kill Seven of Nine. As the crew races against time to save millions of refugees from an imminent stellar cataclysm, the former Borg becomes the target of several seemingly random but potentially lethal "accidents." The investigation reveals a truth more terrifying than anyone ever imagined, as Captain Kathryn Janeway and the crew of the Starship USS Voyager fight for their lives against the most unexpected enemy of all.