Like many of the gentry who find themselves in penury, the Mortmain family is extremely eccentric. Mr Mortmain, a widow, who has recently married again, is a writer, but he hasn't written anything in quite some time because he is suffering from a severe case of writers' block. Years before, his debut novel was a hit around the world, but he has yet to follow it up with anything. Almost a decade before he published Jacob Wrestling he purchased a tumbling and beautiful castle, with a forty year lease, hoping that it would prove to be a place of both solitude and inspiration, but it is now a source of income because the Mortmain's are selling the castle furniture piece by piece so that they can afford to make ends meet.
The family are all rather odd; the new Mrs Mortmain, Topaz, is an artist's model who enjoys nudity. Mr Mortmain's two daughters, Rose and Cassandra, both have literary ambitions of their own, although Cassandra's are more practical than Rose's. Rose sees herself as the romantic heroin of an Austen novel, and wants to live in the castle until her beau comes along. Cassandra journals constantly, anxious to practice writing whenever she can.
As well as the Mortmain girls, there is a son, Thomas, who spends most of his time with Stephen, whose mother was the Mortmain's maid before she died. Stephen still lives with the family. He has a crush on Cassandra and believes himself to be crazy in love with her, and although she is flattered, she does not feel the same way about him, and feels rather awkward in his presence.
When the Cotton family inherit Scoatney Hall, they become the Mortmain's new landlords. There are two Cotton sons, Simon and Neil, with whom Rose and Cassandra are immediately fascinated, not least because neither of the brothers is married. Neil was raised in California and wants to own a ranch. Simon was raised in New England and so has slightly less outdoorsy ambitions; he loves learning and is bookish, like his mother. Simon is the oldest and therefore the heir to the Cotton fortune, which makes Rose find him attractive when under normal circumstances she would not. She decides that she is going to capture his heart, marry him and lead her family out of poverty.
The Cottons initially find the Mortmains extremely entertaining. However, Rose has a detrimental effect on the relationship between the families when she flirts with Simon so inexpertly that she makes a fool out of herself. This is an immediate turn-off to the brothers. They leave, vowing not to have anything more to do with any of the family. However, ultimately the families do become friends, and genuine feelings develop between Simon and Rose, against all the odds. Simon proposes to her after a whirlwind romance.
There is much excitement surrounding Rose and Simon's upcoming wedding. Rose and Topaz travel to London with Mrs Cotton, leaving Cassandra and Simon the only members of either family at home. There is a spark between them and they share a kiss. Simon feels that he could love Cassandra forever, and she fears that she feels the same way about him. She also feels extremely guilty about falling in love with her sisters' fiance and decides that she will henceforth rebuff all attempts at love from Simon. To take her mind of the situation she decides to enlist the help of Thomas in helping her father break through his writer's block They lock him in the castle's medieval tower, hoping that this will force him to snap out of his funk and start writing again.
Cassandra is so preoccupied with her own inappropriate feelings for her future brother-in-law that she completely fails to pick up on the signs that point to Rose's feelings for Neil. This is not entirely due to lack of interest on her part, and partially due to the fact that in order to deflect everyone's attention from their mutual attraction, Rose and Neil have decided to pretend that they cannot stand each other. Their plan works, but they break Simon's heart when they elope, seemingly out of the blue. Simon feels betrayed, but Cassandra secretly hopes the end of his engagement will prompt him to focus on his feelings for her. However, she feels that he is still too consumed with love for Rose and so does not tell him how she really feels when he visits with her before returning to America. Knowing that he plans to return, Cassandra vows to wait for him, and tells him that she will remain faithful to him in his absence.
