Gyro Gearloose has invented a "universal solvent", a thick, black liquid capable of instantly dissolving anything except diamonds. Scrooge McDuck buys the solvent from him, intending on using it in mining. However, in his enthusiasm, Scrooge carelessly pours the solvent directly onto the ground, where it eats a shaft all the way down to the centre of the Earth.
After Huey, Dewey and Louie explain the potentially catastrophic impact of this act - it would eventually lead to the Earth's destruction - Scrooge, Donald and the boys go on a quest down the shaft to retrieve the solvent. What follows is an underground adventure along the lines of Jules Verne's Journey to the Centre of the Earth but more realistic.
In the end, Scrooge deems the solvent as a failed investment. While it did succeed in getting him thousands of flawless diamonds from the bowels of the Earth, he didn't take into account that these diamonds are super-dense, and thus even the smallest ones weigh over 100 kg each, making them useless as jewellery.
This story was inspired by the movie Journey to the Center of the Earth and was based on a The Pertwillaby Papers adventure titled Vortex.