The Challengers investigate the appearance of a mysterious castle. They use a bomb to blow it up, leaving no trace of the structure. Back at HQ, Rocky announces he's quitting the Challs due to headaches he's been having since the explosion. Later, Ace, Red, and Prof have a run-in with the Quadruple Man, but he vanishes. Rocky's doctor reveals Rocky has a metal sliver in his skull which leads the Challs to a castle where they find a helmet capable of turning thoughts into matter. The helmet produces a manifestation of fear but Ace uses the helmet to create four ghost-Challengers to defeat it.; On a routine mission, a seaquake avalanche traps Prof and his sub. Prof is stuck and he can't ditch a bomb, which will explode in two hours. Ace lowers a cable and hook, but the cable snaps. Red rappels down the seamount to trigger another bomb, but is rattled off. Prof asks Rocky to quit rather than get hurt. Rocky screams, “Think!” Prof recalls other times they were trapped by a Cyclops and the Flying Fishman. Prof tells Rocky to swing the ship’s anchor cable and knock the sub free. Prof ditches the bomb and Prof and Rocky get clear before the bomb explodes.