Book #6 of the Star Trek: The Lost Era series.
Set in the year of 2360.
She was trained to be a killing machine. Abandoned as a child, without home or family, past or future, Zetha survived only by her own cunning in the back alleys of Romulus before being taken by the Tal Shiar and remade into one of its deadliest weapons. But Zetha is about to undertake a mission unlike any in her experience. The mysterious return of a virulent scourge thought to be long extinct threatens devastation on a scale almost too horrific to contemplate. Zetha’s only hope of stopping it is across the Neutral Zone—among the enemies of Romulus. Now Admiral Uhura, centenarian chief of Starfleet Intelligence, must decide what to do with the knowledge Zetha has risked her life to bring to her."
Luther Sloan has a very small but very interesting part at the end.