The troubles begin when, in the absence of Lord Epping, his young partner, Dennis and the latter's Aunt Della open up Eppings' country estate to entertain a pair of visitors who have come from Canada to see the absent-minded nobleman. Unknown to any of them, the cellar of the big house has been taken over by a gang of enemy saboteurs making a supply of nitroglycerin so they can blow up a big dam nearby. Hoping to drive away the guests in order to continue their deadly task, the enemy agents create a number of "ghostly" incidents.