Michael G. Jacob, under the pseudonym of Michael Gregorio, writes, along with his Italian wife, Daniela De Gregorio, a historical mystery series influenced by the ideas of Prussian philosopher Immanuel Kant, the latest of which is A Visible Darkness (Reviews, Jan. 12).

How did the series originate?

It all began with Kant. Daniela was teaching philosophy, and she was fascinated by the man and by his ideas. The idea for a short story had begun to take shape in Daniela's head, and we talked it over together. I thought it was a great idea. So great, indeed, that I persuaded her that we—not she alone—ought to turn the story into a full-length novel, which became Critique of Criminal Reason [St. Martin's Minotaur, 2006].

What interested you about Prussia?

As we began to plan the novels, we were fascinated by Königsberg, the Baltic city in which Kant once lived, and by Prussia, a nation which no longer exists. We set out to recreate Königsberg as it might have been at the start of the 19th century. It was an incredible period: the Age of Enlightenment, the French Revolution, the rise and fall of Napoleon Bonaparte, and the Encyclopedia, which charted rapidly expanding knowledge in the sciences. We tried to imagine how some of these developments played out in the Prussia of that period, and felt that other people would be equally fascinated if we could work these themes into a plot which would thrill the reader.

What surprised you the most when you researched Prussia?

Prussian society was an amazing blend of conservative militarism and startling new ideas. And when the French invaded Prussia in 1806, these contrasts were accentuated. The French brought liberty and equality to a country rigidly stratified into masters and serfs. A serf could be whipped by his master for disobedience or hung for stealing an egg. Hair-raising stuff!

How do you split the writing duties?

We work very hard on an initial outline to provide a solid structure capable of carrying a story over 400 pages. At that point, we both have a go at writing the first chapter. Daniela insists that I'm good at describing places, people and things, while she's better at handling dialogue and psychology. She writes her chapters, I write mine; I then add a richer description to the scenes in her chapters; she adds depth to my weak characterization and pep to my conversations. It's a perfect symbiosis in which we are both allowed to do our best. I write in English and translate her chapters from Italian.