The play tells the story of Nikolai Ivanov, a man struggling to regain his former glory. For the past five years, he has been married to Anna Petrovna, a disinherited 'jewess', who has become very ill. Ivanov's estate is run by a distant relative, Mikhail Borkin, who is frequently advising people on how he can help them make money. The doctor, Lvov, an 'honest' man as he frequently reminds the rest of the cast, informs Ivanov that his wife is dying of Tuberculosis, and that she needs to recover by going to the Crimea. Unfortunately, Ivanov is unable, and unwilling, to pay for the trip. He is heavily in debt and already owes Zinaida Lebedeva 9000 roubles. Ivanov is criticised for heartlessness and for spending time with the Lebedevs instead of his seriously ill wife. At the end of Act One, Ivanov departs to visit the Lebedevs', and unbeknown to him is followed by Anna and Lvov.
Act Two shows a party at Lebedevs', and features various people discussing Ivanov. They say his only motive for marrying Anna was for the large dowry; however, when she married him, she was forced to convert from Judaism to Russian Orthodox and was disowned. Lebedev is married to Zinaida, who manages his money-lending, and they have a daughter, Sasha, who is infatuated with Ivanov. She throws herself at Ivanov and he is unable to resist: the act concludes with the two kissing. Unfortunately, Anna arrives unexpectedly at just this moment and witnesses the betrayal.
Act Three shows a number of conversations between Ivanov and other members of the cast â Lebedev begs Ivanov to repay his debts, and Lvov confronts Ivanov once again about the heartless way he treats Anna. Sasha then appears, concerned by Ivanov's refusal to visit since the incident at the end of Act Two. The act then ends with Anna confronting Ivanov about Sasha's visit, and about how he has lied and cheated on her for the entirety of their marriage. Ivanov's anger is aroused by the false accusation and in a fit of anger he reveals to her that she is dying.
Act Four occurs around a year after the previous acts. Anna has died, and Ivanov and Sasha are preparing to marry. As the wedding is about to begin, Lvov appears, planning to unveil Ivanov's 'evil' intentions â believing Ivanov is simply marrying Sasha for the dowry. He makes the accusation publicly and even though other characters have previously expressed doubts they all leap to Ivanov's defence and challenge Lvov to duels. Ivanov finds the whole situation amusing, returning to his old self, and takes out his gun. Sasha realises what he is about to do, but is unable to stop him: Ivanov runs away from the crowd and shoots himself, abruptly ending the play.

Question: Why did Nikolai's marriage plans to Anna get ruined?
Answer: She had to change religions, which invalidated her dowry Nikolai was expecting to receive
Alternative answer: He ends up killing himself