Etienne Cloquet, a young woodsman, is in love with Marie, the pretty daughter of Paul Le Groux, a salmon fisher. Etienne has such a sunny disposition that he has become generally known as "Etienne of the Glad Heart." Notwithstanding his sunny disposition, he has a fierce temper when aroused, so that those who know him realize that it will not do to press him too far. The plans for the marriage of the young couple have all been arranged, and Etienne goes to the lumber camp to put in a final winter with the expectation that he will have enough money saved in the spring so that he and Marie can marry. Olaf, a young trapper, is a handsome fellow, but unscrupulous. He chances on to the cabin of Paul, and becomes a boarder with the family. Naturally, he is attracted by Marie, and realizing her engagement to Etienne. plans to gain her affections. One of Etienne's accomplishments is the playing of the guitar, and it has been his custom to carry this instrument with him when he visited his sweetheart. They discover that Olaf is even a superior performer on the guitar, and Marie begins to show an interest in him as a result of his pleasant ways and musical skill. During Etienne's absence in the lumber camp Olaf makes progress in the winning of Marie, her parents being unsuspicious of the change in her affections. While Etienne is in the lumber camp he rescues an Indian named Peter from a terrible death, and Peter has become his faithful friend. Peter accompanies Etienne on his return from the lumber camp. Just about the time of Etienne's return, old Paul becomes suspicious of Marie, and discovers her in the act of sewing a tiny garment which confirms his suspicions that there is something wrong. Paul demands the attendance of Etienne, believing him to be the culprit, and wishing to bring him face to face with the disgraced girl. At the cabin door, they meet Olaf returning from a trapping trip. They face Marie and Paul commands that his daughter shall name her betrayer. Marie is overwhelmed with shame, and does not speak. Etienne, to whom the information is wholly new, at once grasps the situation, and springing upon Olaf, endeavors to kill him with his bare hands. Marie's mother intervenes and saves Olaf's life. The disgraced girl is driven from home, accompanied by Olaf, her betrayer. The home-like cabin of Paul becomes a place of sorrow. Etienne has lost his spirit, and one night he takes his beloved guitar into the woods and hides it. Peter, believing that Etienne will once more be happy, rescues the guitar and takes it to the cabin, unknown to Etienne. The love of the mother impels her to urge Etienne to undertake a search for Marie. She misses her only child, and her heart yearns for her. She has not had word of her for months, and does not know whether Marie be alive or dead. Etienne consults with his friend Peter, and it is finally decided that a search shall be made for the outcast girl. Peter finally locates the cabin in which Olaf and Marie are living. He accompanies Etienne to the place, and they find the couple inside. Olaf's heartless and brutal treatment of Marie enrages Etienne, but Peter restrains him. They watch the cabin in secret until Olaf goes for an inspection of his traps. Then they hurriedly enter the cabin, urge the overjoyed girl to escape under their protection and the three hasten away and embark in Peter's canoe for the return trip. They are going to take Marie back home. Olaf returns unexpectedly to the cabin a short time after their departure. He notes the absence of Marie and cannot understand it. His skill in woodcraft discloses the tracks of Marie and her two companions, and he follows the trail to the river. There he notes the marks which show that another canoe has been hauled up at the landing. Furious with rage, he springs into his canoe, and follows with all the haste and speed that his skill can supply. Down the winding river he follows the heavily loaded canoe containing the girl and her two friends. Etienne and Peter are also experts at the battle, but the added weight in their canoe renders their progress slower than that of their frantic pursuer. Olaf finally gets within range, and pulling his six-shooter, he empties it at the occupants of the canoe. They proceed uninjured, and throwing the now useless weapon away, he continues to paddle after them. The leading canoe is propelled to the shore, and Marie and Etienne disembark in haste. Olaf drifts past undecided as to what his next step shall be, but Peter, realizing what the friendship of Etienne means to him and what the despicable acts of Olaf in connection with Marie have meant to his friend, he dashes after Olaf, and upon arriving alongside, he launches himself like a catapult on the shoulders of the doomed Olaf, upsetting the canoe, and both floundering into the ice-cold stream. Peter returns alone. The anxious mother accepts the return of Marie with all of a mother's love. Gruff old Paul accepts the situation, while Etienne, with the sunshine once more in his heart, accepts his rescued guitar from the grinning Peter, and happy hearts beat once again.