Ned ignores Dr. Gordon's warning about keeping Jonah the pony away from yew leaves, which could poison him. When Jonah does indeed become sick, Dr. Gordon cannot leave John Danby's ailing wife, so it is up to Jenny, Ned, and Black Beauty to save the pony's life.

Mr. Joskins is selling quack remedies and Dr. Gordon intervenes after they make several of his patients ill. To get revenge Joskins tampers with Beauty's girth strap which injures Kevin while he is riding. Albert intially blames saddle maker Surtees but ultimately discovers the true villain.