They had little formal schooling. Their emotionally detached Edwardian parents, who sent their only son to Eton, thought education was wasted on girls, who were expected to marry well. Deborah, the youngest, called Debo, grew up with governesses, tutors and servants in country seats, a London house and an island in Scotland. Despite the trappings, the family’s wealth was shaky and in the Depression years required economies.

From age 6, Deborah had a passion for chickens. In their drafty old Oxfordshire manse, she and her sisters hid in a linen cupboard heated by water pipes and made up secret languages. Her father, an irascible baron, hunted his children on horseback, with hounds. Visiting Munich with Unity in 1937, Deborah, 17, wrote home: “We have had quite a nice time here & we’ve had tea with Hitler & seen all the other sights.”

At 21, she married Andrew Cavendish, second son of the 10th Duke of Devonshire. His older brother was killed in World War II, and when his father died in 1950, he became the 11th Duke, inheriting vast wealth, including a castle in Ireland and Chatsworth, a 35,000-acre Derbyshire estate that had been in his family for generations.

Surrounded by 105 acres of gardens designed by Capability Brown and miles of meadows and wooded hills, Chatsworth’s magnificent 16th-century mansion, with ceilings painted by Antonio Verrio, had 297 rooms, 112 fireplaces, 68 lavatories, 26 baths, 32 kitchens and workshops, 17 staircases, and 1.3 acres of roof.

But it came with a catch: inheritance taxes of nearly $20 million, not to mention huge maintenance costs. Like many of Britain’s great country houses fallen on hard times, Chatsworth, outmoded and rundown, had long been open to the public, but its trickle of visitors and income left the duke and duchess in the red. They sold artworks and acreage to pay taxes totaling 80 percent of the estate’s value: $285 million in today’s money.