In the play, we learn that, due to straitened circumstances, Captain Ronald Dancy has given his Rosemary filly to Ferdinand de Levis. Dancy is a war hero, albeit a penniless one. He can no longer afford his stables and horses. At a party given by his friend, Charles Winsor, in Meldon Court, Dancy discovers to his consternation that de Levis has sold his prized filly for a thousand pounds. Ferdinand is also a guest at Meldon Court.
When de Levis tells Winsor that he has had a lot of money stolen (to the tune of nearly one thousand nine hundred and seventy pounds), Winsor is incredulous and embarrassed. After all, de Levis is not suggesting any of his guests stole the money, is he? The affair of the stolen cash is the catalyst for bringing to the surface all the latent prejudices of Winsor's guests. The usual good humor extended to de Levis is nearly obliterated by an incident which exposes all the ugly suspicions and anti-semitic envy in Winsor's guests.
For one, Winsor shocks Lady Adela with his prejudice when he stresses that de Levin 'pushes himself' unwisely into circles that he really doesn't have a right to belong to. He reassures Lady Adela that he likes Jews; however, he still believes that a Jew should know his place. In Winsor's opinion, pushing oneself toward membership in the exclusive (and aptly named) Jockey Club doesn't speak well for de Levin's sense of decorum. "Jockey" can be a noun, describing one who rides in horse races, or a verb, describing a struggle to achieve some particular goal. It is obvious that the distasteful notion of a Jew 'jockeying' his way into established circles is anathema to Winsor's wealthy guests. The fact that de Levis is also a wealthy man in his own right escapes the Mayfair set: wealth alone is no guarantee of acceptance in their fairly entrenched circle.
The implication that de Levis is a bad sport is also evident in Winsor's speech when he describes de Levis' sneering response to losing a bet with Dancy. It is obvious that Winsor is irritated by de Levin's lack of respect toward his superiors.
WINSOR. Standing jump on to a bookcase four feet high. De Levis had to pay up, and sneered at him for making money by parlour tricks. That young Jew gets himself disliked.
When Lady Mabel urges de Levin to retract his charges against her husband, Dancy, de Levin stands strong. He is not moved when Lady Mabel tries to appeal to him to remember his place as a gentleman and 'to behave to us as you would we should behave to you.' He is under no illusions as to this manipulative and disingenuous plea, reasoning that, under any other circumstances, he would only be 'a damned Jew' among Lady Mable's set.
Mrs. Dancy, I am not a gentleman, I am only a—damned Jew. Yesterday I might possibly have withdrawn to spare you. But when my race is insulted I have nothing to say to your husband...
Conveniently for everyone, St. Erth also suspends de Levin's membership application to the Jockey Club while the police investigation continues.
DE LEVIS. [Tremulous with anger] Don't trouble yourselves about my membership. I resign it. [To DANCY] You called me a damned Jew. My race was old when you were all savages. I am proud to be a Jew. Au revoir, in the Courts.
The above are but a few examples of the suspicion and discrimination de Levin endures as a Jew in the play. Hope this helps.