Jim Black, learning that his rival, David Durard, son of Colonel Durard, wealthy Southern wholesale grocers, has won the heart of Marion, plans to separate the lovers before war breaks out. Not long after war is declared and David is given the captaincy of a company. Before David leaves for the front. Jim takes an actress friend, Miss Gordon, into his plot and has a letter written to David asking him to call upon the actress at eleven o'clock if he wants to secure some valuable information. Another letter is written to Marion telling her to be around the house mentioned in the letter at eleven o'clock if she wishes to avoid an unhappy marriage and to learn of the unfaithfulness of her sweetheart. David arrives at the house at the stated time, and in accordance with Jim's plot, Miss Gordon suddenly becomes sick and falls into the arms of David, just as Marion appears. She observes the actress in her lover's arms, and, taking it for granted that he is only having her as a plaything, returns home and sends back their engagement ring with a note that it is all over between them. David comes for an explanation, but Marion will not receive him. Four years later David is instructed by General Lee, who has taken his headquarters in the Durard mansion in Petersburg, to gain information concerning General Grant's plan to wipe out his starving army. Following out their pre-arranged plan, Old Mammy, the Durard's old servant, is chased by some Confederate soldiers dressed as overseers into the Union camp. Informing the Union soldiers that she has run away from a cruel master, they take her to the officers' headquarters, where she is given work. She hears that Grant contemplates making an attack on the left wing of Lee's army, and bringing into play the secret code made between herself and the Confederate soldiers, hangs certain wearing apparel in certain positions along the clothes line. This is observed by the far away Southerners through their field glasses, and Lee makes a very successful attack. Marion, whose home is near Petersburg, and which is within the Federal lines, has been entertaining some Union soldiers. On one occasion, when Nelson, a Union captain, was playing with her little sister, a note drops out of his pocket, which gives the information that Colonel Mosby's cavalry is coming to reinforce Lee's army. Marion makes a copy of the message and hurries to the Confederate lines. She reaches Lee, who forthwith details David with a dispatch for Col. Mosby to hurry along. Unable to get to her home, Marion becomes a nurse in Lee's army. In the meantime General Grant has held a secret meeting in order to discover the leak of information. Suspicion rests upon Old Mammy, their suspicions are confirmed when Old Mammy is caught reading her code. She is court-martialed and shot. In order to deceive Lee, Grant has certain clothes placed in such positions on the line, which, when interpreted, convey the information that Grant is going to attack the left wing of Lee's army, when in reality he is planning to attack the right. Lee's army is being badly annihilated when Col. Mosby's cavalry arrives and drives the Unions back. Jim Black is badly wounded, and just before he dies makes a confession to Marion of how he estranged her and her lover. The battle still rages and Col. Mosby mines the bridge. As darkness sets in, there is cessation in the hostilities. David is shot in the shoulder and is brought to the field hospital for treatment, where he meets Marion. He learns of Jim's confession and forgives Marion for her past actions towards him.