Barely escaping death, Gunter is surprised when his investigation uncovers more advanced war technology being developed by the Confederates. Angamar, an enigmatic old scientist, connives to include Gunter into his development of a self-propelled torpedo, and Gunter discovers the reincarnation of his own first engineering project, a submarine.
The Confederate submarine experiment evolves into the H.L. Hunley, and Gunter, using the alias Sam Miller, is consumed with the desire to become part of her crew. When the Hunley is called up for duty as a blockade breaker in Charleston, South Carolina, Gunter is forced to choose between loyalty to his homeland, the submersible, and an attractive war widow.