Frank and Joe go to the Pocono Mountains to investigate the mystery of a legendary witch who stalks Black Hollow seeking vengeance. Disappearances occur and strange screams fill the night.
Frank and Joe Hardy become involved in a large and dangerous conspiracy while trying to keep the valuable invention created by one of their father's clients from falling into the hands of thieves.
Young detectives Frank and Joe Hardy, investigating the disappearance of a professor, encounter a hot-tempered hermit, and sabotage at the radar station and Honeycomb Caves.
