Double Helix, Book 3.
Like the biological weapons they employ, a sinister conspiracy has spread across the Delta Quadrant and across many years of Starfleet History. Now the mysterious menace surfaces again – to strike at the heart of the Romulan Empire.
An artificial virus has infected the entire Romulan ruling family. Ambassador Spock must put aside his efforts at unification to summon his old friend, Dr. Leonard McCoy, who discovers that the only hope for a cure lies with a long lost Romulan heir whose blood and tissues have not been contaminated by the virus. But can the heir be found before the collapse of a ruling dynasty throws the entire Empire into chaos?
Diane Carey (born 1954) is an author of historical fiction and science fiction who is perhaps best known for her work in the Star Trek franchise. She is the co-creator, with John J. Ordover, of the spin-off series, Star Trek: New Earth, and its continuation series, Star Trek: Challenger.
Among her other Star Trek novels are the original series books Star Trek: First Frontier, Starfleet Academy, the Starfleet Academy novel Cadet Kirk, the Star Trek: The Next Generation novel Ghost Ship, and the Star Trek: Deep Space Nine novelization of the two-part episode "The Way of the Warrior."
Diane Carey. Wikipedia.