Billy Garrison, a successful young jockey, rides the favorite "Sis" in the Louisville Derby. He does not ride with his customary vigor and dash. He feels "doped" and entirely out of condition and as a consequence "Sis," instead of winning the race, trails in last under the wire. At the stables he is accused of throwing the race, but denies it. stating that something was the matter with the horse and himself. He can only conjecture that the drinking water had been "doped" before the race. George Waterbury, owner of "Sis," rages over the loss of the race, which costs him a pot of money. In his anger he threatens to thrash Garrison, but Jim Drake, an honest, successful horseman and a good friend of Garrison, prevents Waterbury from carrying out his intentions. Drake does not believe Garrison to be guilty of throwing the race. Garrison starts for the city heartbroken over the accusation. At the railroad station he interferes with a ruffian who is forcing his unwelcome attentions upon Sue Desha, daughter of a well-known horseman, and thereby wins her favor, but their acquaintance is merely casual and neither expects to see the other again. Garrison enters a café, and there learns that the police are searching for him on the charge of poisoning the running horse, "Sis." Jim Drake enters the café, learns of his predicament, offers him money with which to leave the country and declares his friendship. Garrison refuses to go away and says he is determined to face the accusation. Drake leaves the café and then Garrison overhears two men at an opposite table repeating in a loud voice the charges that Garrison had thrown the race. The little jockey becomes infuriated and knocks one of them down, but the other man strikes Garrison on the head with an empty wine bottle, knocking him to the floor senseless and bleeding. Garrison is taken to a hospital, unidentified and delirious. He remains in the hospital for several weeks and when his wounds have healed he recovers his physical strength, but his mind is a blank. He wanders about aimlessly until, while in swimming one day, an unscrupulous lawyer determines to profit by the similarity of a birthmark on the jockey's arm. A reward has been offered for information as to the whereabouts of a young man bearing a similar birthmark. Snark, the lawyer, determines to profit by what he thinks to be a coincidence, and in his weakened mental condition Garrison falls a victim to the wiles of Snarks and agrees to enter into the deception, so that Snarks will receive the reward. Garrison is received into the family of Major Calvert as the missing nephew, William Dagget. Sue Desha visits the Calvert home, recognizes Billy, and they fall in love. But Billy's conscience bothers him and he decides to go away. On his way back to the city the train is wrecked and he again receives a wound on the head. The shock of the railroad wreck has relieved a brain lesion, so that a piece of the skull which had been pressing upon the brain cells is released and the hospital surgeons remove it. Billy Garrison finds himself weak and emaciated, while the happy months spent by him in the beautiful home of Major Calvert are a blank. Jim Drake, his old-time friend, traces Garrison to the hospital and finds him there. He is overjoyed to find the young jockey recovering his health and arranges with him to ride the favorite "Speedway," of which he is owner, at the coming Carter Handicap. Strengthened by the knowledge that his friends are still loyal and heartened by the prospects of again entering into the racing game, Billy recovers rapidly and in a short time is able to leave the hospital. In the meantime Wm. Dagget, a brother-in-law of Major Calvert, sends him word that his son, Billy, who disappeared some time ago, has been riding as a jockey under the name of Billy Garrison. The Major again makes every effort to discover the missing young man, but finds no trace of him up to the day of the great race. Colonel Desha, the father of Sue, finds himself in financial straits; his ill luck at the race track and his continued confidence in his own stable having cost him many thousands of dollars, so that his entry carries his entire fortune. If his entry loses, the Colonel will be a broken man, while his daughter, Sue, must forego her pleasant life, of social enjoyment. On the day of the race, honest old Jim Drake accidentally discovers the financial crisis which threatens to wreck the life of his friend, Colonel Desha. Drake is not too well supplied with this world's goods, but he has a heart as big as a haystack and he plans to aid the Colonel in his distress. There is only one way to accomplish this. He withdraws "Speedway" from the entries and by this scratching of the favorite, the field is left open for a probable conquest by the thoroughbred entry from the stable of Colonel Desha. Drake realizes that there is no jockey the equal of Billy Garrison, so when he withdraws "Speedway" from the Carter Handicap, Garrison is released and instructed to ride the Desha entry. Around the track they go, and in this most exciting finish, Billy pushes his mount to the front and triumphantly wins the race and purse for the Colonel. There is great excitement. Sue recognizes Billy as the young man in whose care she had entrusted her heart, but Billy, unconscious of what has passed during the period of his mental aberration, does not recognize her, although he is instinctively drawn to her. Jim Drake informs Major Calvert that Billy Garrison is his long lost nephew. The crooked stable man who doped "Sis" and Garrison and caused all the trouble confesses; explanations are made all around and everybody is happy. Billy Garrison has won life's handicap.