A young inventor builds a steel submarine intended to travel beneath polar ice and, accompanied by two loyal assistants, mounts a perilous expedition toward the North Pole. The narrative blends detailed descriptions of the vessel and its mechanisms with episodes of underwater navigation, iceberg hazards, a sunken wreck discovery, and clashes with villainous pursuers and Arctic inhabitants. The crew struggles with entrapment, repairs, and survival under extreme conditions, passes beneath an ice barrier into an open polar sea, and conducts exploratory forays across icy terrain before the expedition reaches its concluding outcome.