Initially, Joe Green is the stable boy for Squire Gordon and Lady Anne at Birtwick Park; he replaces James, who in Chapter 16, after the Squire and his wife have decided to visit friends and stay at an inn, rescues Beauty and Ginger from burning after a careless man has entered the barn, smoking a pipe. In Chapter 17 the fifteen-year-old Joe begins work under the tutelage of James. Because he is so small, the only horse he can groom is little Merrylegs.
Then, in Chapter 18, Beauty is made to race to Doctor White's in town because Mrs. Gordon falls ill. Squire Gordon tells John to let the horse rest at the Inn and then return. But, Dr. White's horse is spent and he must ride Beauty back to Birtwick. Upon their return, Beauty is covered with sweat:
My legs shook un me and I could only stand and pant. I had not a dry hair on my body, the water ran down my legs, and I steamed all over....Poor Joe! He was young and small, and as yet he knew very little, and his father, who would have helped him, had been sent to the next village.
He rubbed Beauty down, but did not put a blanket on him. Innocently, he gave Beauty corn and then cold water to drink. Of course, Beauty becomes sick and has an inflammation in his lungs and a fever, but he recovers after a time. This episode is used by Sewell as a lesson about how detrimental to a horse ignorance is. John thinks that "it is the worst thing in the world, next to wickedness."
Further, in Chapter 20 while Joe is on an errand with Beauty, he comes across a cruel man beating his horse because it cannot pull a terribly heavy load. The drunken man curses the boy; Joe hastens to the home of Mr. Clay, a brickmaker, who hastens to the scene. Later, Joe is called in to the Squire, who is a magistrate, and testifies to what he has witnessed. Action is taken against the cruel owner. This episode, too, contains a moral lesson on drunkenness and inhumanness.
At the end of the novel, it is Joe Green who works for the Blomefield sisters when they purchase Beauty from Mr. Thoroughgood, who has nursed the broken horse back to health. As Joe grooms Beauty, he recognizes the star on his forehead, the one white mark on his front leg, and his scar from having been bled. Elated to find Beauty, he informs the sisters about the horse, and they write to Mrs. Gordon to tell her that Beauty has come to them.