•Why it earns a slot
Northanger Abbey is Austen's sustained comic argument that the novel is a serious literary form, defended explicitly in Chapter 5 and dramatised throughout by showing how Gothic fiction both misleads and, ultimately, educates a reader who learns to apply imagination with judgment rather than without it.
Seventeen-year-old Catherine Morland, a clergyman's daughter with no heroic qualities, travels to Bath and then to the Gothic abbey home of the Tilney family, where her imagination, inflamed by Gothic novels, leads her to suspect the respectable General Tilney of murdering his wife. When Henry Tilney gently exposes the absurdity of her suspicions, Catherine is humbled into common sense, and the novel ends with the General's mercenary scheming exposed and Catherine and Henry married.
This distillation is written from the freely available original, which is always the better read when you have the time: gutenberg.org.