The Dome of the Rock in Jerusalem has been blown to bits by extremists, and, in retaliation, thousands have died in another major attack on the United States. Now the FBI has been dispatched to deal with a new menace. A plague targeted to ethnic groups—Jews or Muslims or both—has the potential to wipe out entire populations. But the FBI itself is under political assault. There's a good chance agents William Griffin, Fouad Al-Husam, and Jane...