Star Trek: The Next Generation: Double Helix #3: Red Sector

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?