The action of this story takes place more than twenty years after Northanger Abbey. John Thorpe is still unmarried and still a blustering braggart. He runs into Colonel Frederick Tilney in Bath who complains about the country estate that is his inheritance. It seems that he, his wife and younger daughter prefer the society of London and fashionable watering places to the country. When Thorpe happens to be in the neighborhood, he visits the Abbey as a friend of the Master. Returning to Bath, he informs the Colonel that many repairs are needed there. Under the influence of too much wine, Tilney gives Thorpe authority to make needed changes to the estate. John Thorpe then moves to Northanger to make these improvements.
Isabella Thorpe Firth is the impoverished widow of a man who was disowned by his family. She visits from relative to relative until they so tire of her that she is asked to leave. She has just been removed from her sister Anne's home, so invites herself to stay with her brother at Northanger Abbey. Being very bored with the country, she invites her 20-year old son, Roland to come. Roland is tutor to a crippled 14-year old boy. He must obey his mother but cannot desert his charge, so brings Charles Ballard with him. Isabella is still the consummate flirt, trying to attract the attention of any adult male she encounters.
Soon after the invasion of the Thorpes, Paulina Tilney, the eldest daughter of the Colonel, comes home while the rest of her family goes abroad. She loves the Abbey and spends as much time as she can. She is accompanied by her "uncle", the devout clergyman, James Morland.
John Thorpe wreaks havoc on the estate with his diggings in search of a chapel that must be restored. After a few adventures, Paulina must return to her family and tells her father what is going on at Northanger. Colonel Tilney insists that all are interlopers; that he authorized no such undertaking. He then returns to NA and demands that everyone leave. Things are quickly wrapped up when the authorization note is presented, love is discovered and all ends well.
I found Uninvited Guests to be a quick and pleasant read.