What's a good nonfiction about nobles and intrigue?

Read about Sir Francis Walsingham.

I don't know how well this fits your interest, but a great history set in Medieval times is A Distant Mirror, by Barbara Tuchman. Set mainly in France, as I recall.

caw

May want to read up on the Gunpowder Plot.

A good idea would be to look up what periods in history famous fantasy study themselves for inspiration. George R.R. Martin has stated numerous times that the plot to Game of Thrones was inspired by England's War of the Roses.

But personally, I think the entire Tudor lineage is fascinating: Henry VIII, Mary I, Elizabeth !, the entire conflict of Protestants vs Catholics. Makes for some very exciting reading.

Fiction, but obsessively researched: Dorothy Dunnett's 'Lymond' and 'Niccolo' series. Features many real people and events of Late Medieval and Renaissance periods. Kick ass plots.

blacbird beat me to it; Tuchman's "A Distant Mirror."

There's plenty there about the rise of the noble class, medieval economics and and geopolitics, with a mini ice-age and the Black Death thrown in too.

The Deadly Sisterhood might be a start?

Try The Fronde by Orest Ranum -- an intensely complex set of noble intrigues (& civil war) in France during the minority of Louis XIV.

Look up the author Conn Iggulden, novels based on history with some creative liberties taken. He has a series about Julius Ceasar, one about Genghis Khan, one ongoing series based on the war of the roses.

You might want to check out Dr. Ian Mortimer's books. He has several books on history. I currently have two - The Time Traveler's Guide to Medieval England and The Time Traveler's Guide to Elizabethian England. Both are good introductions to what you would've seen, smelled, eaten, worn in the time period indicated.

Wolf Hall, by Hillary Mantel.

The Accursed Kings. This series of historical novels set in Medieval France was one of George R.R. Martin's main inspirations for A Song of Ice and Fire.

Maurice Druon's Accursed Kings series (vol. 1 is The Iron King) is among the finest historical fiction ever, well-researched & well worth reading. But if the OP is looking for non-fiction, this isn't it. (Nor for that matter, are Wolf Hall or Dunnett's Lymond & Niccolo series, all of which are also very good historical fiction.)