In an effort to protect the environment, the students of Bayport High have organized a massive recycling campaign -- Project Planet Earth. Even the industrial giant United Plastics has expressed support for the idea. But someone has developed a more sinister plan -- a campaign of sabotage designed to poison the entire project.

Frank and Joe's investigation turns urgent when the dirty tricks turn deadly. A United Plastics security guard is crushed in a factory machine, and the Hardys have evidence of blackmail and murder. But they won't be able to prove a thing until they put their own lives at risk...penetrating the company's defenses and uncovering the darkest, dirtiest secret of all!