Three years ago, Sebastian Faulks was in Los Angeles when he felt the call of Paris.

“I had this feeling that there was something for me there,” he tells me over coffee in central London.

“I wanted to go and immerse myself in the city so, in spring 2016, I went there for two months. I had an idea for a novel about one character who looks at Paris through ignorant eyes and another character who is well-informed. I walked the streets and travelled on the Metro, imagining I was my characters and...