Paul, a European war orphan who is the ward of his mother's childhood friend, Mrs. Graham, whose husband was also killed in the war, has difficulty adjusting to his new life in a rural area of the U.S. Haunted by the air raid death of his parents and brother, Paul remains aloof at school, insecure about his language skills and his ability to fit in with the other children. Afraid that Paul will be taken away by the authorities if they are not happy together, Mrs. Graham sends him to spend the summer with Father Matthew at the Santa Ynez Mission in California, hoping the priest will help him. Paul quickly adjusts to his job as caretaker of the mission's animals and even uses newly acquired American slang in his conversations with the animals. When a stray German Shepherd named Rin Tin Tin arrives at the mission, Paul grows to love him. He confides in the dog about his loss of faith because of the destruction of his family and village. After a few weeks, Rin Tin Tin's stern owner, Mr. Melrose, retrieves the dog, and Paul is heartbroken because he is convinced that he loses everything he loves. While Rin Tin Tin repeatedly attempts to escape and return to the mission, Father Matthew encourages Paul to have faith, assuring him that no one in America wants to hurt him, but that they want to be his friend. One night, when Melrose arrives to retrieve Rin Tin Tin, Paul hides him in the barn loft. When the hay in the loft catches fire, Rin Tin Tin adroitly douses a rag with water and puts out the fire before being rescued. Melrose then gives Paul a stern warning that he must shun Rin Tin Tin if he comes back or he will beat the dog to teach him a lesson. As Rin Tin Tin makes his next escape attempt, Melrose beats him with a club, inciting the dog to bite him and flee again to the mission. This time, with Melrose's threat ringing in his ears, Paul sadly shuns the dog, who lopes off to the nearby woods. That night, Paul prays to God that Rin Tin Tin will return. Melrose arrives at the misson in a rage and demands that Father Matthew put down Rin Tin Tin because he is rabid. While searching for the dog in the dark woods, Melrose is attacked by a wild dog and is saved by Rin Tin Tin, who then leads Father Matthew and Paul into the woods to rescue him. Later, Melrose gives Rin Tin Tin to Paul, and no longer afraid of people, Paul attends Mass at the mission for the first time.