The eccentic figure of The Potter is well known in Rocky Beach. But when the old man with his flowing robes and bare feet suddenly vanishes, the Three Investigators are mystified. What is the connection between The Potter's past, a royal family and a revolution? The symbol of the two-headed eagle is the clue. In probing the mystery, the boys come face to face with a deadly rival. But how can they combat an unseen enemy who leaves only his footprints behind - burning imprints of human feet?