In The Saracen’s Mark (Atlantic, May.), Perry’s Elizabethan sleuth, physician Nicholas Shelby, must solve murders in London and Morocco.

How did this series originate?

I’d written a historical novel set in ancient Rome, which got rave rejections from publishers. I would have given up on getting published if it hadn’t been for their supportive comments. So I decided to have one last attempt, and set the story in Elizabethan London. Being a Londoner and a Shakespeare fan, I have a soft spot for Southwark, where the Rose and the Globe playhouses were, and which was the city’s red light district at the time of Queen Elizabeth I.

What about this era fascinates you?

It was a time of great upheaval, the shift from the medieval into the early modern. Religion was a paramount factor in every single person’s life. In England, we went from Catholic to Protestant, back to Catholic and then to Protestant again, all in barely 50 years. From the scientific aspect, it’s the dawn of the modern world. Physicians are beginning to challenge the erroneous assumptions of the past—the purpose of even the heart isn’t understood. And astronomers are starting to think the unthinkable—that the earth is not the center of the cosmos.

Why make your lead a physician?

I wanted my lead to be very competent in his own world, but also beset by self-doubt. What better than a physician? This is a time when medicine is based on assumptions made by ancient Greeks and Romans. Nicholas is good at the practical side of what he does, having been a surgeon in the war in the Spanish Netherlands. He can treat wounds and fix bones. But he learns that all the theory he’s been taught about how the body works and how it should be healed is based on ignorance. When he needs it most, it fails him. He has to rediscover his own self-worth.

Where did the idea for the Moroccan part of the story come from?

I wanted to get Nicholas out of Southwark—just for a change, really. In my research for the other books, I’d learned there was a company set up in London in the late 16th century to trade with what was then called the Barbary Shore—modern-day Algeria and Morocco. A visit by a Moroccan envoy to London had made the exotic fashions and manners of the people they referred to as Moors very popular. There was a political element to this relationship, too. Despite the fact that in the eyes of each nation, the other was heathen, they both had Catholic Spain as an enemy.