The Three Investigators set out to find Mr. Allen's Irish setter, one of six dogs missing from the neighborhood of Seaside, but he insists there is a dragon living in the cave in the cliff under his house. More interested in the dragon than the missing canines, Jupiter, Pete, and Bob explore the cave—and come face-to-face with the terrifying dragon! Chased by menacing scuba divers on the beach and by an eccentric neighbor on the cliff, The Three Investigators plunge into a case where danger lurks at every turn. The Three Investigators must decide, are they willing to risk their lives and return to the cave to for the clues they need to solve The Mystery of the Coughing Dragon?