Episode Title:
X Marks the Spot.
Episode Description:
During a trip to England, the gang meets Professor Isaac Belfour, who has created an invisibility potion. Professor Belfour's former assistant, who stole the potion and used it on himself to embark on a life of crime, now calls himself Mr. X and is intent on stopping Professor Belfour from developing an antidote to the potion. Loosely based on The Invisible Man.
