End of Casefile#4: The Hardys are proud of Fenton Hardy's past as a New York City cop. But when an enemy from the old days turns up, Frank and Joe face a danger that could kill millions -- starting with their kidnapped father! Hidden bombs in the air conditioning systems of Manhattan skyscrapers are set to go off. The explosions eill spread a deadly virus to everyone in the buildings. It's a monstrous plot and a deadly challenge. Can Frank and Joe stop this plot and save their father?

Back of Book: In the middle of a gala political banquet, Fenton Hardy is kidnapped. Then a mysterious caller outlines his terrifying demand: unless he receives twenty million dollars, Fenton Hardy -- along with many thousands of innocent victms -- will be infected with a fatal virus. New York City will turn into a ghost town! Police Chief Sam Peterson, Hardy's ex-partner in the NYPD, immediately takes charge. His first official act is to order Frank and Joe off the case. But the brother detectives are too worried about their father to heed the chief's warning -- even if it means entering a strange underground world far below the city streets. A world where darkness rules, the mob is the only law, and murder lurks behind every shadow.