Catherine Morland is a fairly unremarkable seventeen-year-old living in a small village, Fullerton, with her nine siblings and her parents. Fortunately for Catherine, this boring state of affairs only lasts one chapter. The Allens, a well-off childless couple, invite Catherine to visit tourist hot-spot Bath (a resort town in England) with them. Catherine is thrilled to get out of her dull town. But Catherine's views of life outside of her small town are highly colored by the romantic Gothic novels she reads, as well her own inexperience and naiveté. This leads to a lot of comedic mishaps during her time away from home.
While in Bath, Catherine meets and befriends two families: the scheming Thorpes and the wealthy, educated Tilneys. She first meets the charming and witty Henry Tilney at a ball and quickly develops a huge crush on him. Luckily, Catherine also befriends Isabella Thorpe, so she has someone with whom to discuss her crush. Isabella and Catherine bond quickly and go on a spree of reading Gothic novels, gossiping, and attending balls.
Isabella is also in love with Catherine's older brother James. And James is good friends with Isabella's older brother, John. So, naturally, the Thorpes decide that Catherine is the perfect match for John. They can all double date. John is, unfortunately (and hilariously), rude and overbearing. The Thorpe siblings spend their time manipulating both James and Catherine in order to ensure advantageous marriages for themselves. While the Morlands are certainly not rich, they do have more money than the Thorpes. Catherine remains largely oblivious to the Thorpe's schemes and tends to assume that everyone is as honest as herself and James. This leads to a whole series of comedic mishaps where the naive Catherine continually manages to extricate herself from situations orchestrated by the Thorpes.
Despite John's ham-fisted attempts at wooing and Isabella's shrewd efforts at distraction, Catherine is still falling in love with the wealthy Henry Tilney. She also befriends his polite and quiet sister Eleanor, who is the polar opposite of the artificial Isabella. While Catherine grows closer to Henry, Isabella gets engaged to James. But, within a few days, Isabella meets the handsome Captain Tilney, Henry's older brother, and begins to flirt outrageously with him.
Henry, Eleanor, and their father, General Tilney, decide to leave Bath and invite Catherine to visit them at their home, Northanger Abbey. While at Northanger Abbey, Catherine's love of Gothic novels and her tendency to confuse fiction with reality come back to haunt her. Catherine makes some bad assumptions after hearing of Mrs. Tilney's death, and she begins to suspect the controlling General Tilney of murder. Henry calls her out on this, and Catherine feels bad when she learns that Mrs. Tilney died of perfectly natural causes.
After this, Catherine also learns that James has called off his engagement to Isabella. Isabella had embarked on a relationship with Captain Tilney, but, unfortunately for her, Captain Tilney has no marriage plans. Isabella is socially ruined by this scandal and Catherine realizes that their friendship was a sham.
Things are going well with Henry and Catherine, however. But, before their relationship can progress towards an engagement, General Tilney throws Catherine out of his house. Catherine is confused and returns home to Fullerton. But Henry follows, explaining that his father learned that Catherine wasn't as rich as he had thought, which meant they could no longer socialize. Against his father's wishes, Henry proposes to Catherine. Eleanor, meanwhile, marries a wealthy man, and General Tilney soon gives his approval to Henry and Catherine. Henry and Catherine then marry. The End.