Mr. Harrel is married to Cecelia's childhood friend, Priscilla. So, Priscilla gives parties to introduce Cecelia to new friends: Sir Robert Floyer, Mrs. Harrel’s shy brother Mr. Arnott, Mr. Gosport, silly Miss Larolles; and proud, silent Miss Leeson. Mr. Monckton visits her and she greets him happily. At an opera, Cecelia sees Albany, the strange old man again. He shouts a warning that she is in danger from the people around her and that she should help the poor. The next morning, she sees a poor woman, Mrs. Hill, who comes to beg for her starving family. Mr. Harrel has refused to pay them. Cecilia tries to make him pay, but he will not. Finally, Mr. Arnott, feeling sorry for the Hills, lends him the money to pay them. Cecilia, shocked at how mean Mr. Harrel is, wants to go stay with another guardian. But, they seem just as bad. While Mr. Harrel spends and gambles his money; Mr. Briggs is a selfish miser and Mr. Delvile is a vain man.
Mrs. Harrel has a masquerade ball. Mr. Monckton is in disguise as a black demon and fights anyone who comes near Cecelia.. A person dressed like a white domino tries to help her, as do Mr. Arnott, Mr. Gosport, and Mr. Belfield. Cecilia is surprised at how well the domino knows the faults of her guardians. She wonders who he could be. Later, Cecelia goes to the opera again with Mrs. Harrel. There, she meets Mr. Belfield, who is courteous; but Sir Floyer acts rudely. The two men get angry and have an argument that leads to a duel. Afraid, Cecilia hurries to her house, and worries over the duel.
The next morning, Cecelia is told that Mr. Belfield is a little injured, but Sir Floyer is well. Cecilia finds out that the white domino she saw at the masquerade party is Mortimer, Mr. Delvile’s son. Soon after, she meets Mrs. Delvile, who she likes. Now she wants to stay with them, instead of with the Harrels. But, she discovers that Mortimer thinks that she is in love with Mr. Belfield. Or perhaps, that she is engaged to Sir Floyer, who has asked her to marry him. Even though she has refused him, Mr. Harrel tells everyone they will be married soon. Later, she meets Mr. Albany again, who introduces her to Belfield's sister, Henrietta, and asks Cecilia to help her. Cecilia finds out that Mr. Belfield’s wound is serious, but because he does not have enough money he could not call a doctor. She helps the Belfields, begins a friendship with Henrietta, and finds out that Mortimer Delvile, too, is helping them. Disgusted with Sir Floyer’s rudeness and the Harrels’ silliness, she stays for a while with Mrs. Delvile, whom she has become fond of, and Mortimer. But, Mr. Monckton tells lies about them because he sees Cecelia likes them. But Cecilia does not believe him, and she realizes that she is in love with Mortimer, who still thinks she is engaged to Sir Floyer.
Mr. Harrel threatens her with his own suicide, so Cecilia lends him money for his debts. Mr. Delvile is suddenly called away, and Mortimer is happy and surprised to find out that Cecelia loves him. But, when she meets him again she is hurt by his coldness to her. Mr. Harrel loses more money by gambling and his violent behavior to his wife frightens Cecilia. After drinking, he suddenly kisses his wife and shoots himself. Terrified and upset, Cecilia meets Mortimer, who forgets to be cold. He travels with her and Mrs. Harrel to Delvile Castle, where Cecilia finds Mortimer’s behavior confusing, and Mrs. Delvile makes it clear that she does not want Cecilia to marry her son. Lady Honoria, a relative of Mrs. Delvile’s, comes and teases her about Mortimer. At last, Mortimer says that he cannot marry her, because he would have to change his name from Delvile to Beverley. He is too sad to see her anymore and he leaves the country. Cecilia says goodbye to him coolly. Mrs. Delvile, instead of going to see her son, goes to her family friend, Mrs. Charlton, and stays with her instead. While there, Mr. Biddulph, a friend of Mortimer's, sees with surprise that she is embarrassed whenever he talks about his friend, and tells that to Mortimer in a letter. Confused, Mortimer decides to find out for himself. Lady Honoria steals Mortimer’s dog, Fidel, and gives it to Cecilia to tease her. One day, Cecilia, patting the dog, talks to him about her love for Mortimer, and how much she misses him – and looking up, sees—Mortimer!
Amazed that she loves him, he asks her to marry him. Cecelia is confused, and cannot hide how much she loves him; but she is angry when he suggests that they marry in secret. He explains that his parents will never allow their marriage. So, even though Cecilia is afraid and feels guilty, she says yes. She innocently tells Mr. Monckton about her plans. He becomes furious and tries his best to break them up. During the wedding, he sends Miss Bennet, Lady Margaret’s servant, and his helper, to interrupt it. Mrs. Delvile, hearing of it, comes and tells Cecilia that what Mortimer says is true – she will never let them marry. Cecilia is unhappy, but she loves Mrs. Delvile too much to make her hate her, and finally agrees that she will not marry Mortimer. but he insists on seeing her again. Because of this, all three came together for a last meeting. Mortimer begs Cecilia to be his wife, and says he doesn’t care if he is Mr. Beverley or not. Mrs. Delvile, horrified, suddenly falls very sick. Both Mortimer and Cecilia are frightened, so they decide to do as she says, and never meet again.
Mrs. Delvile, after kissing Cecilia goodbye, leaves as soon as she is better. The next day Mrs. Charlton suddenly dies. These events cause Cecelia to be sad and lonely, so she leaves for London. Because she is now old enough to have her fortune, she buys a quiet house in her neighborhood and lives there with Henrietta Belfield. Mortimer suddenly visits them. Cecelia finds out that Mrs. Delvile has said that if she will give up her fortune, so Mortimer will not be Mr. Beverley, but Mr. Delvile, she can marry her son. Mortimer happily says that they can marry with just her personal fortune. Cecilia, horrified, tells him that she has none of her personal fortune left. She has lent most of it to Mr. Harrel, and used the rest for other things, such as helping the Hills. Cecilia also finds out that somebody has told this to Mr. Delvile already, but with lots of lies. She begins to suspect Mr. Monckton. Mrs. Delvile says yes and Cecilia and Mortimer marry quietly and happily.
Later, Mrs. Matt, one of the poor people she has helped, tells her who stopped her first wedding—Miss Bennet! Cecilia decides that the person who sent her must have been Mr. Monckton. She also realizes that he, too, must have been the one who lied so bitterly about her to Mr. Delvile. Shortly after, a servant comes and tells her that Mr. Monckton is dead. Soon after, Mortimer comes and says he too had found out Mr. Monckton’s meanness, and he had angrily told Mr. Monckton to tell Mr. Delvile the truth about Cecilia. Mr. Monckton angrily said no, and they shot each other in a furious fight. Mortimer was safe, but Mr. Monckton was badly hurt. Cecilia tells him to leave England with his mother before she can hear about the fight, and agreeing, he goes. However, her marriage has been discovered, so her fortune is taken away from her while Mortimer is gone. Now unable to live in the house she bought, she tells Henrietta to live with Mrs. Harrel and Mr. Arnott while she looks for Mortimer. Cecelia goes to Mr. Belfield to ask for help; but while there, Mortimer suddenly walks into the room and sees them together.