The narrative follows two teenage cousins who, after surviving a runaway car wreck, become involved with their inventor father in designing and testing an experimental diving torpedo boat called the White Shark. Their work triggers strange discoveries, confrontations with shadowy antagonists, and perilous sea episodes that include fog, naval encounters, and an encounter with a mysterious water creature. The boys conduct model trials, stage rescues, decipher urgent messages, and outwit an enemy before a climactic maritime showdown. Mechanical ingenuity, youthful daring, and a sequence of escalating crises drive the plot to a final rescue and resolution.