Private Dennis Reilly has followed his horse, Sergeant Murphy, into the army and when Murphy is transferred to the cavalry, Dennis transfers also. Because he wants the horse to be discharged from the army when his own enlistment is finished, Dennis coaches Murphy to act wild so he will not be considered a good cavalry horse. Col. Carruthers thinks Murphy has potential, however, and sends him back to school. Meeting the attractive Mary Lou Carruthers while he is exercising Murphy, Dennis tells her Murphy's story without realizing that she is the colonel's daughter. Now that she knows the truth, Mary Lou is able to take Murphy successfully through his paces. She offers to help Dennis buy Murphy from the army after he leaves, but when Murphy is injured on a jump, the colonel is forced to sell him sooner. Dennis is prohibited from owning the horse as long as he is in the army and the colonel refuses to postpone the auction until he is discharged. Dennis spends the last ten days of his enlistment in the guardhouse and as soon as he is released he obtains the address of Murphy's new owner, intending to buy him back at any price. He finds that Murphy was too wild for his new owners, who sold him in their turn. Finally he tracks Murphy to a dog food company and arrives just in time to save him from death. Dennis then enters Murphy in steeplechase races and wins regularly. He does so well that they sail to England to race in the Grand National, but when inspectors find ticks on the animals in the cargo of the boat, Murphy is placed in quarantine. Desperate, Dennis sneaks Murphy off the boat by forcing him to swim to shore. After a near miss, Murphy wins the race, and the colonel, who is attending with Mary Lou, is forced to wear her hat and ride Murphy to the winner's circle as a penalty for betting against him.