During a heavy storm, a tree fell on Kirrin Cottage - meaning with the cottage out of action, the Famous Five travel to stay with Mr. Lenoir - an acclaimed scientist and colleague of Uncle Quentin, who lives at Smuggler's Top. Lenoir has developed a plan to drain the surrounding swamps - bit Mr. Barling, a nearby rival, wants to stop him, so he kidnaps Uncle Quentin and Sooty, Mr. Lenoir's son. It's up to the Famous Five to get them back.
—Darren Harrison