Disaster seems imminent when scientists discover that the planet Mongo is about to crash into Earth. Luckily, heroic young Flash Gordon is on hand to lead an investigative mission into outer space and onto the speedily approaching planet. There, he and his best girl, Dale, who is along for the ride, learn that Ming, the devious ruler of Mongo, has purposely put the planet on a collision course with Earth, and only Flash can stop him.
A group of 21st-century colonists inhabit an underwater city called Pacifica. Originally intended as a purely scientific installation, the U. S. government wants to stash all its gold reserves from Fort Knox there, along with a fantastic new radioactive element. The brother of Pacifica's returning former commander plans to steal the gold and on top of that, the city faces destruction by an asteroid from outer space!
Nu er Ariel tilbage, denne gang er hun blevet alvorlig og voksen, og det er derfor hendes 12-årige datter Melody, der er den centrale hovedfigur. Som spæd var Melody en fingerspids fra at ende i fangarmene på Ursulas fæle søster Morgana, så Ariel svor på, at datteren aldrig måtte komme i nærheden af havet og Morgana igen. Men man kan ikke bekæmpe sine instinkter. Melody elsker havet, som var hun en fisk, og da hun tror moren hader havet og ikke kan forstå hendes længsel efter de åbne hav, lusker hun i det store blå uden at fortælle nogen om det.
Survivors of a sinking ship are rescued by Captain Nemo and his submarine crew. They are taken to an underwater city where they may spend the rest of their lives.
On a volcanic island near the Kingdom of Hetvia rules Count Dakkar, a benevolent leader and scientist who has eliminated class distinction among the island's inhabitants. Dakkar, his sister Sonia and her fiance, engineer Nicolai Roget have designed a submarine which Roget pilots on its initial voyage just before the island is overrun by Baron Falon, despotic ruler of Hetvia. Falon sets out after Roget in a second submarine and the two craft, diving to the ocean's floor, discover a strange land populated by dragons, giant squid and an eerie undiscovered humanoid race.
An engineer, a psychologist and several other disparate types take part in an experiment to see if people can live for extended periods of time in a city built under the ocean.