Frank and Joe race Seattle to help their father Fenton, who stands accused of murder! In their father's rented house, they're met by burglars, who try to gun them down. When the brother detectives follow their trail, they learn that valuable timber is being destroyed by a deadly virus. They also find an entire town has been sealed off to prevent a mysterious flu epidemic. Meanwhile Fenton Hardy is the hostage of a sinister scientist with a formula for certain death. And if the brother team can't reach him in time -- he'll become the victim in a doomsday experiment.