After finding a mysterious message inscribed on a plumb bob found inside a piece of lava, Prof. Lindenbrook and his student Alec McEwen mount an expedition to descend into the Snaeffel-Jokull, an extinct volcano in Iceland. They are joined by Hans, a native guide, and Mrs. Goetaborg, the widow of Lindenbrook's rival. In addition to the natural menaces of the trip into the Earth's interior, they must also contend with another explorer, Count Saknussemm, who is determined to be the only one to return.