“I think it’s the subject, don’t you?” said Antonia Fraser’s publicist on the way to an interview in 1969. The extraordinary success of Mary Queen of Scots had put them all on the back foot. Few people had expected the 36-year-old daughter of Lord and Lady Longford – and married mother of six – to write serious history. She had contributed to a children’s series for Marks & Spencer (arrows whistled, steeds galloped, flags fluttered) and she had written books about toys and dolls. Before a three-year stint working with the publisher George Weidenfeld, she had moped about Fenwick’s department store, selling hats and grousing to the Evening Standard diarist about uncomfortable shoes and antisocial hours. “Is it one of those so-s