Maryland Calvert lives in that section of Maryland divided against itself in the question of secession. Her brother Floyd is so strong a Northern sympathizer that he joins the Federal secret service unknown to his family and enlists in the Southern army to increase his efficiency. Her fiancé, Alan Kendrick, takes a commission in the Federal Army, although his father becomes a general in the Confederate forces. One Thorpe, a discredited Union officer, is given an opportunity to serve the Federal secret service and in that capacity, joins the Confederate army, becoming an aide to General Kendrick, whose headquarters are at the Calvert mansion. Alan Kendrick is among the Northern prisoners taken by the Confederates and when sent for exchange is recognized by Thorpe, whose bitter hatred has been aroused by the part the gallant Unionist had in his former discovery and degradation for conduct unbecoming an officer and a gentleman. Learning the Federal plans of campaign from Lloyd Calvert, who believes him to be a loyal member of the Federal secret service, he takes advantage of this knowledge to attempt the destruction of the Union camp to which Alan Kendrick has been sent, thereby hoping to encompass Alan's death. Thorpe fails, but Alan, taking a desperate chance to visit Maryland Calvert, is captured in a Confederate uniform and sentenced to death as a spy. Maryland Calvert, hysterical over the death of her brother Lloyd, who was shot down while trying to "run the lines" with information, is unconsciously responsible for Alan's denunciation and conviction as a spy. When she realizes his situation, Maryland braves the hazardous ordeal to reach the Union lines and secures from General Hooker a written request upon General Kendrick to delay Alan's execution until facts may be presented proving his innocence of espionage can be established. Her return finds General Kendrick dead on the battlefield, the treacherous Thorpe in supreme command and Alan imprisoned in a church awaiting momentary execution. When Maryland presents her letter to Thorpe he realizes his supreme opportunity for revenge is at hand. He orders a squad to dispatch Alan and proceeds to force his unwelcome attentions upon Maryland. With her lover standing bound before her awaiting death, Maryland is driven to such a frenzy that she plunges a bayonet into Thorpe. He falls unconscious and she releases Alan, gives him Thorpe's hat and coat as a disguise, and bids him fly for his sake as well as her own. A moment later when Thorpe regains consciousness and orders an alarm sounded. Maryland recalls that the old church-bell is the agreed tocsin. Dashing up the creaking stairs she reaches the highest spot in the belfry and clinging to the enormous clapper swings from it in its dizzy flight, using her frail hands as a muffler to kill all sound. The deaf sexton tolls away at the rope unconscious of the fact his labor is in vain. Maryland is made a prisoner and is about to be executed in her own home, when Alan appears at the head of the Union troops. Thorpe would use her as a shield to compel Alan to fire upon his beloved or abandon the attack, but at the crucial moment he is removed from command by order of General Lee, who has learned of his perfidy. Alan Kendrick grants the Confederates a truce to cover their retreat and the drama ends with a blissful reunion of the lovers.