Lack of money has compelled the Duke of Wistburgh to turn his castle into a showplace, but he is not distressed by this so long as he can continue his main interest in life - hunting. He is therefore naturally annoyed when his horse Persimmon one day refuses to take a fence: his annoyance changing to amazement when his butler informs him that his mount would like to have a word with him. The fact is Persimmon has decided he has no longer any taste for hunting; and he does not mince matters in telling the Duke that he has been talking to other horses - from a circus, which by arrangement with the Duke, has taken up its position in the car park - and has joined their trade union. Hunting, he says, is too stenuous compared with trotting round the sawdust ring. The Duke's concern at this revolt naturally gives a wrong impression to his wife, a cheerful ex-musichall star, and his daughter, who both feel that he may be following in the steps of his grandfather who was noted for a mind that was none too strong. But soon they too are convinced when they hear Persimmon's Left Wing views.The Duke, of course, is prepared to do anything to persuade Persimmon to go back to hunting; and in the end the family seek the advice of the hearty cockney circus proprietor Sam Sly, who justifiably thinks at first that they are pulling his leg. Finally convinced there is no trick, he is quick to see the immence financial opportunities of the only talking horse in the world. The Duke is engaged to appear in a double act with Persimmon at a very generous figure and great publicity is given to the performance. Disappointment, however, follows for Persimmon perversely refuses to say a word in public. In fact the experience of appearing in the circus ring causes him to change his mind about trade unionism and the easy life, and he decides to go back to hunting and never talk again. The Duke is happy at last, especially as, resulting from the publicity, the National Trust are going to take over the castle's expenses. Sam's initial resentment at being let down gives way to delight when Persimmon makes amends and whispers to him in confidence that he has everything fixed to win the next Grand National.