From the moment Tom swift finds himself tossed about helplessly in an undersea geyser to the time he faces possible death at the hands of his enemies, the young scientist fights to overcome many obstacles in putting his two latest inventions to use.

When Tom discovers that helium on the ocean bottom had caused a geyser, he plunges into the task of building an underwater city of derricks and pipelines to capture the gas. His astounding new water-repelling machine and phenomenal hydrodome make the gigantic operation possible.

While at work at the undersea mountain site, Tom and his pal Bud Barclay uncover what seems to be a pirate treasure, but find in the leaden chests a cache of death-dealing destruction. Time and again the young scientist's plans are nearly wrecked. A sinister, hooded figure attacks him in his laboratory, and a mysterious submarine nearly costs him his life.