Joe Green is learning quickly; he is attentive and careful in his work. John now trusts him with many tasks, but the boy is small and does not regularly care for or ride either Black Beauty or Ginger. One day John is out with Justice when the master needs a note delivered to a gentleman who lives about three miles away. He instructs Joe to saddle Black Beauty and ride him carefully to the gentleman’s house.
They deliver the note without incident. On their way home, they see a cart laden with bricks which has gotten stuck in the mud. As they approach the scene, the driver is shouting at the horses and beating them mercilessly. It is a sad sight; the horses strain and sweat, trying without success to pull the cart from the mud while the man continues to swear at them and beat them brutally.
Joe tries to reason with the man, but he does not stop, telling the boy to mind his own business. It is clear the man has been drinking; caught up in his anger and frustration, he will not listen. Joe turns Black Beauty toward Mr. Clay's house, and they move with greater haste than the master would approve of, to be sure; however, both horse and rider are eager to put a stop to the man’s abusive behavior.
Mr. Clay, the brickmaker, is a friend of the Squire. When Joe arrives at his door, Mr. Clay wonders if Joe has brought a message from him. Joe explains what is happening in his brickyard, and Mr. Clay immediately prepares to go to the scene. He asks Joe if he would be willing to testify to what he has witnessed if the matter should go to court. Joe says he would be glad to speak the truth.
When Joe and Black Beauty return home, John asks why Joe looks and acts so angry. Joe quickly tells the story, and it is wonderful to see the quiet young boy roused to such passion. John assures the boy he did the proper thing, unlike many others who would not have stopped. Cruelty and oppression are everyone’s business, according to John, and when a person sees them, he should do what he can to stop them. "[Y]ou did right, my boy," he tells Joe. Now Joe is calm. He basks in the older man’s praise. Just before dinner, Joe learns he has been summoned to the Squire’s private room to give evidence of a man abusing his horses. The boy’s eyes sparkle as he agrees to tell what he saw.
John helps the boy straighten his clothes a bit before sending him to the master. The Squire is one of the local magistrates, so the matter has been brought directly to him for settlement. There is no word from Joe until he returns to the stable and celebrates with Black Beauty. The boy gave his testimony clearly, and the condition of the horses was so deplorable and obvious that the abuser was immediately sentenced to several months in prison. Joe seems to have grown an inch. He is as kind and gentle as he has ever been, but now there is purpose and determination behind his actions—as if he has made the transition from boy to man.