After Sue shows off her newly learned ability to create invisible force fields and turn others invisible, the FF has to deal with constant complaints from the city and public officials who are concerned with the FF's constant (and potentially dangerous) scientific experiments. Deciding that maybe it's best to find an island away from the city to store their equipment, the group checks out an island that is up for sale.
There they find a cavern that brings them face to face with the first foe they ever faced: The Mole Man, who has survived their previous encounter. After a battle against his Moloids, the FF are captured and made prisoners after learning of the Moleman's plot to sink the world's largest cities below the Earth. Escaping from their specially made cells, Reed rewires the Mole Man's before escaping the island. When the Mole Man activates the device it causes his own island to sink destroying his device in the process.

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