Can you tell me a bit about your first encounter with Agatha Christie’s work? 

I don’t have a lovely origin story. She’s always been there as far as I can remember. I think she is sort of like the wallpaper in a lot of people’s lives. I do remember checking out an Agatha Christie as a treat from the library at the start of my school holidays. I remember getting The Blue Train just after finishing my GCSEs and diving in and sitting in a chair until I’d finished it.

You mention the Christie Archive in your book. I wondered if you could tell me about using those to research your work? 

Well, if you had met Agatha Christie in person, she could be shy and withdrawn and watchful. But on paper, perhaps because she was a writer, she was so different. She was chatty and exuberant and vulnerable. Reading her correspondence was amazing. There’s this rollercoaster of correspondence when she’s trying to decide whether or not to marry her second husband. I was completely gripped by that. He was 14 years younger than her and there were all sorts of reasons not to marry him. Anyway, eventually her ten-year-old daughter worked out what was going on. And my favourite letter says, ‘Rosie’ (that was the daughter’s name) ‘has guessed about the proposal, and she will give her consent to the marriage, if you send by written two dozen toffee lollipops from Selfridges.’

All ten-year-olds should be required to negotiate marriage . . . 

on behalf of their parents. Yes. 

In terms of the tour you’re doing, how did you go about condensing a life that rich into a show which is just under two hours? 

It’s really hard. I've been panicking about it all summer. All my family members have heard the show in various draft forms. At one point my dad said, ‘well, I didn't fall asleep’, which is high praise from him. 

It’s clear from your book you want to confront head-on the problematic nature of some of Christie’s novels, for example, the subjects of class and race. Are there any of her books that you consider too problematic to still be part of her canon? 

No, I don’t. I think, actually, the trouble is when people read these books just expecting entertainment. That’s when your expectations confront an uncomfortable reality. But we should read them because they are records of social history as well. And we need to know what people thought; we need to know how prevalent these attitudes were, so that we can confront that and make the present better. It’s light and shade, warts and all. Don’t look away. Learn about the past.

Do you think Agatha Christie’s legacy might be different if she was a man? Would she be taken more seriously?

That’s hard to answer because she wouldn’t have written the way she wrote unless she was female. There’s been a whole strand of 20th-century criticism which is to position yourself as a highbrow person by giving Agatha Christie a kicking. But it’s often said the bestselling books in history are Shakespeare, the Bible and Christie. What I find astonishing is that no one ever follows that by saying, ‘she did that in a world made by men’. And the fact that her stories are crime stories, and that they are middlebrow; she was very proud of being middlebrow. When she got one of her many honours (I think it was Dame Commander) she said, ‘that’s one up for the lowbrows’.

She owned it? 

She did, and she also had problems making any claims for her work. I’m pretty sure this is partly to do with her gender and her Victorian upbringing, but also to do with this big public shaming she had in 1926 [Christie triggered a national manhunt when she left home, abandoned her car and mysteriously disappeared for 11 days, prompting headlines around the world]. Before then, you do see her making statements about her ambition and career. But after 1926, she always talks of herself as a lucky little old lady. 

Are there any other authors you would like to see re-evaluated, particularly women? 

Monica Dickens, Barbara Pym, Rosamond Lehmann, Elizabeth Bowen, Elizabeth Taylor, Elizabeth Jane Howard. Mid-century, middlebrow female novelists are a favourite of mine. I'm not ashamed to enjoy their work. 

I’m going to ask you a really horrible question to finish. Do you have a favourite of Christie’s books? 

I’m going to go for Murder At The Vicarage because it introduces my favourite Christie character, Miss Marple. What’s brilliant about Murder At The Vicarage is that to the first readers, they wouldn’t even have known that this slightly funny old lady was the detective. I mean, we know it’s Miss Marple. But you wouldn’t know that if you were picking up the first edition of that book. This week, I’ve been thinking about a picture of Agatha Christie, the Queen Of Crime, meeting the actual Queen at the film premiere of Death On The Nile. I’ve been thinking about indomitability and longevity and the way that you mustn't underestimate little old ladies.

An Evening With Lucy Worsley On Agatha Christie, Assembly Rooms, Edinburgh, Sunday 9 October; Agatha Christie: A Very Elusive Woman is out now, published by Hodder & Stoughton.