During the Civil War, Captain Lewis K.  Dumont, an expert telegrapher for the Northern army, disguises himself as a Confederate and crosses enemy lines in order to provoke the fall of Richmond.  He rescues Southern officer Howard Varney and falls in love with his sister Edith Varney.  Lewis' brother Henry allows himself to be captured in order to convey information to Lewis.

Benton Arrelsford, a rejected suitor of Edith's and the head of the Confederate Secret Service, believes Lewis is a spy, and sets a trap by allowing Henry to escape.  Lewis and Henry are brought together in the Varney home, and Lewis shoots his brother as an escaped prisoner of war.

Lewis is finally trapped by Arrelsford, arrested, and sentenced to die.  The North captures Richmond, and Edith and Lewis are reunited.