On a rescue mission sparked by a tip about Commodore Schmidlapp aboard his yacht, Batman and Robin race to the scene in the Batcopter. The yacht vanishes beneath them, and Batman resurfaces with a shark biting his leg, which he quells with bat-shark repellent as the creature explodes in a splash of foam. Back at Commissioner Gordon's office, the Dynamic Duo deduce that the tip was a trap laid by the United Underworld, a cabal of Gotham City’s most formidable criminals: the Joker, the Penguin, the Riddler, and Catwoman.
The quartet arm themselves with a dehydrator that can turn people into dust for later rehydration and slip away in a war-surplus, pre-atomic submarine crafted to resemble a penguin. They recruit three pirate-themed henchmen—Bluebeard, Morgan, and Quetch—and set their plan in motion. Batman and Robin learn the yacht was really a holographic projection, and they race back via Batboat to a buoy concealing a projector, only to be trapped there by a magnet and targeted by torpedoes. A radio-detonator helps them blow up two torpedoes, while a porpoise makes the ultimate sacrifice to intercept the last one.
Catwoman, in disguising as the Soviet journalist Kitka, helps the group kidnap Bruce Wayne and pretends to be kidnapped alongside him, part of Penguin’s scheme to finish Batman with another of his explosive animals—unaware that Bruce Wayne is Batman. Bruce fights his way free, slips back into the Batman guise, and the Dynamic Duo return to the United Underworld HQ, only to discover a smoking bomb in their path.
The Penguin, masquerading as the Commodore, infiltrates the Batcave with five dehydrated henchmen. The plan collapses when the henchmen dissolve into antimatter after being rehydrated with toxic heavy water used to recharge the Batcave’s atomic pile, leaving them dangerously unstable. The heroes then confront the kidnapping of the dehydrated United World Organization Security Council, as ambassadors from Japan, the U.S., the U.S.S.R., Israel, France, Spain, West Germany, the United Kingdom, and Nigeria are pulled into the danger. A chase ensues in the Batboat to recover them and Miss Kitka, and [Robin] uses a sonic charge to disable the Penguin’s submarine, leading to a tense fistfight on the surface.
In a dramatic turn, Batman discovers that Kitka is Catwoman when her mask comes off. Commodore Schmidlapp’s sneeze shatters the powder vials, scattering the Council’s dust. Batman then devises an elaborate Super Molecular Dust Separator to filter the mingled grains, while Robin wonders aloud whether the dust could be altered so that humans can no longer harm one another. Batman, however, reminds him that altering human nature isn’t something they can achieve, citing the fate of the Penguin’s unstable henchmen, and rather than change people, they hope for a peaceful coexistence.
With the world watching, the Security Council is re-hydrated and restored—all alive and well, yet each member suddenly speaks the language and exhibits the mannerisms of a different nation. The Dynamic Duo quietly hopes this strange mingling of minds might promote understanding, then slip away from United World Headquarters by climbing out a window and descending on their bat-ropes.
