In Harrison’s Murder in the Cathedral (Severn, Sept.), the Reverend Mother Aquinas investigates the double poisoning of an Anglican archdeacon and a seven-year-old boy in 1920s Cork, Ireland.

Why did you choose a religious figure as the protagonist?

I chose a woman of power, and a very highly respected person in the city. Up to a decade or two previously, the Catholic church was subject to serious restrictions in Ireland, which were only completely lifted when Ireland attained complete freedom in the 1920s. The result of this persecution was that religious figures who had suffered, and even died for their faith, were held in very high esteem in the Ireland of the 1920s, and they had a very strong influence, especially amongst the working class.

How does that make her a plausible sleuth?

The problem, I’ve always felt, with Agatha Christie’s Miss Marple lies in her credibility, in the respect which is accorded to her opinions. That would not have been the case with the Reverend Mother. Also, she is not just an aged spinster with a sharp brain; she had power, managed a business, with a budget and a staff which would exceed that of most businesses in the city. And she would have had immense respect from the people of the city; the poor because of what she did for them, and the wealthy, because of her status.

How is writing about the Reverend Mother different from writing about Mara, your other female protagonist, a 16th-century judge?

I know her so very much better. The Reverend Mother is more of my own present age. She does the same job as I, though in a secular way, did when I was a head teacher of a school in England. Where she had the bishop to restrict her spending and to curb her initiatives, I had the county council. And I did subtly battle with them throughout my career as a head teacher, just as she battles with the bishop.

How representative of her time is the Reverend Mother’s profound empathy for her city’s poor?

Well, this is meant to be a tough one, I think. Deep down you may well be accusing me of sentimentality and anachronism. But I’m going to stand up for myself. I think her character is valid. I do think that she could have thought like that. When it comes to empathy, I can say that my own father, though a solicitor, and the son of a very wealthy man, had an immense sympathy with the poor and spent a lot of time visiting and distributing alms, gifts of food, and clothing among the slum buildings of Cork.