- "Evil forces lurk in the shadows of the Hardys hometown!"
- — Tag-line, from 1988 cover
Detective Sam Radley is found incoherent, wondering the woods on the Morton farm just outside Bayport. Then Sam is kidnapped from his hospital bed. Meanwhile, his boss, the famed PI, Fenton Hardy is away, investigating an attempted sabotage on the Alaskan pipeline, so it's up to Fenton's sons, Frank and Joe to solve the mystery of Sam Radley's disappearance.
The brothers' investigation leads them to a supposedly deserted mansion, on the neighboring propriety to the Morton's farm. Frank and Joe discover a deadly weapon which has been captured by the criminal cult, behind the would-be sabotage in Alaska. Their only hope now is to uncover the mystery hidden within the mansion.