Threat on Cabin Island -- An angry caller -- Missing grandson -- A Christmas visitor -- Two suspects -- Troublesome trio -- Cry for help -- The mysterious messenger -- Warning by code -- Puzzling theft -- A cryptic notation -- An ice boat clue -- The fleeing ghost -- Chimney-top discovery -- The Shah's prize -- The intruder's revenge -- The dangerous climb -- The crash -- A frightened thief -- The hazardous search.

When they are invited to spend Christmas vacation at the private island retreat of wealthy Elroy Jefferson, the Hardy boys become involved in two mysteries: the disappearance of Mr. Jefferson's grandson and the theft of a priceless collection of antique medals.