I wanted to be a female detective – doesn’t every girl?

As a child I always wanted to be George in The Famous Five books: headstrong, brave and daring – the girl who was equal to the boys in solving mysteries, fighting baddies and discovering lost treasure.

After my mother left for Argentina, I was brought up by my father. Ex-military, he loved thrillers and whodunnits, and passed that love on to me. As a teenager I would devour Agatha Christies, thrilled that Miss Marple and Tuppence were as good at solving cases as Hercule Poirot.

In my latest novel, A Most Intriguing Lady, my heroine Mary is a problem solver; a female sleuth, ready to right wrongs and fight injustice. When writing Her Heart for a Compass, my heroine Margaret (Mary’s sister) went on a long train journey. “She’ll need something to pass the time”, I thought.

I did my research and discovered that the railway revolution created a demand for sensationalist crime fiction, sold by WH Smith railway bookshops. The yellowbacks had brightly illustrated covers with a yellow protective covering, and some featured female detectives. I decided Margaret would buy one of those novels and leave it lying around at home for Mary to find.

Intrigued, I continued my research and discovered that these fictional female detectives had real-life counterparts. Women were more easily able to infiltrate a house and gain the confidence of female employers.

This was especially useful when investigating cases of “criminal conversation” (that’s adultery to you and me). A woman servant had access to areas where a male would give rise to suspicion. At first these women were spies employed by male private investigators (often ex-policemen), but by 1875 female PIs were advertising their services in newspapers.

The 1858 Matrimonial Causes Act, which enabled more people to divorce, appears to be responsible for the demand for female PIs. Both men and women could seek a divorce, but they had to prove adultery; and, in the case of women, desertion, bigamy, incest or cruelty. Witnesses had to be willing to stand up in court and testify; to have their names publicised and linked to scandal.

Many early female PIs were actors; mistresses of disguise. Women like Kate Easton, Antonia Moser and Maud West. They were not just employed in divorce cases, but also to expose blackmail, spiritualist and medical fraud, hoisting (shoplifting) and to find missing persons.

Female detectives worked in other areas too. Women were employed in undercover work during the Great Exhibition of 1851. Posing as members of the public, they would watch for people acting suspiciously, and then inform a male police officer who had the power to arrest. Eastern Counties Railway employed female detectives beginning in 1855 to prevent luggage theft.

Frances Power Cobbe of the Sheffield Evening Telegraph wrote of the female detective in the paper’s 13 October 1888 edition: “She would pass unsuspected where a man would be instantly noticed; she would extract gossip from other women much more freely; she could move through the streets and courts without waking the echoes of the pavement with sonorous military tread; and lastly, she would be in a position to employ for whatever it may be worth the gift of intuitive quickness and ‘mother-wit’ with which her sex is commonly credited.”

It was an opportunity for a more exciting, adventurous and varied career offering financial security and independence. A career with a purpose, open to women of all ages and backgrounds.

Women like my heroine, Mary, who could investigate unobtrusively whilst outwardly fulfilling her role as a duke’s daughter in high society. Work where her input was of equal value to a man’s.

Sarah Ferguson is an author and member of the royal family