The story centres around the Ashbys, an English country-squire
family. Their centuries-old family estate is Latchetts, in the fictional
village of Clare near the south coast of England. It takes place in the
1940s, after World War II.
The Ashby family consists of Beatrice Ashby ("Aunt Bee"), a 50-ish
spinster, and the four children of her late brother Bill: Simon, 20;
Eleanor, 18–19; and twins Jane and Ruth, 9. Bill and his wife Nora died
eight years before. Since then, the Ashbys have been short of money. Bee
has kept the estate going by turning the family stable into a
profitable business. The Ashbys breed and sell horses, train horses, and
give riding lessons.
When Simon turns twenty-one, things will change on his inheritance of
a large trust fund left by his mother. He is also the heir to
Latchetts. Simon had an older twin brother, Patrick. Soon after Bill and
Nora died, Patrick disappeared, leaving what was taken as a suicide
note.
The title character, Brat Farrar, is a young man recently returned to
England from America. He was a foundling. At the age of 13, the
orphanage placed him in an office job, but he ran away instead. He ended
up in the western US, where he worked at ranches and stables for
several years, and became an expert horseman until a fall injured his
leg and he was left with a limp.
On a street in London, a complete stranger greets Brat as "Simon". He
is Alec Loding, a second-rate actor. He knows the Ashby family
intimately and sees a way to help his own fortunes. Alec's idea is that
Brat should impersonate the missing twin, Patrick, and as the elder
brother, claim the trust and the estate. Alec remembers a great deal
about the Ashbys, Latchetts, and the village, and this will allow him to
coach Brat on all the background details. In return Brat will give him a
share of the money. Brat is reluctant, but eventually agrees,
especially when he hears about the horses.
After two weeks of tutoring, Brat appears at the office of the Ashby
family solicitor (lawyer), saying he adopted the name "Brat Farrar"
after running away. He gives his own story as the account of Patrick's
missing years. Mr. Sandal informs Bee, who meets Brat and is also
convinced. Over the next two weeks, Sandal verifies Brat's story. The
family receives "Patrick" at Latchetts. His presence leads to the
discovery of Patrick's actual fate, murdered by Simon. The final
confrontation leaves Simon dead and Brat in hospital. There Bee's Uncle
Charles identifies Brat as an illegitimate son of Bee's wastrel cousin
Walter.