I had been writing nonmystery novels set in many periods, without success. My first mystery, and first book which sold, was The Cater Street Hangman . Now I love it for its atmosphere, contrasts between wealth and poverty, what seems to be and what is, for its glamour and squalor, and for the fact that it is largely before the use of science in detection. It is also a mirror of our own time close enough to be valid, and far enough away to be bearable. I get immense pleasure from the manners which are so much subtler than ours, and therefore fun to write about.
Romance can legitimately go on for ages.
I had to research a great deal. Now I hope I know the period well enough to write most of the book with only minor checking, except for whichever subject I have chosen that is unusual to that book. For example, photography will be featured in one that is planned, the workings of the Victorian theatre for the same book, 1890s spiritualism for another, and so on. I love working. I usually begin around nine a.m., break for half an hour's lunch, work again until five p.m. or six p.m., have supper, and often go back for an hour or three in the evening.