In The Professor and the Parson (Counterpoint, Feb.), Sisman traces the long career of a recalcitrant con man.

How did you come to write this book?

I wrote a biography of the historian Hugh Trevor-Roper. In Trevor-Roper’s archive, I found a dossier he had kept on a man known as Robert Peters, tracing Peters’s extraordinary career of fraud from the 1940s to the 1980s, when the dossier ceased. Trevor-Roper himself planned to write a book about Peters, but never did, and it occurred to me recently that I might do so instead. But I wasn’t sure if I’d be able to publish it, as it was conceivable that Peters was still alive, and he was notoriously trigger-happy, threatening legal action against anyone who said or wrote anything against him. I was able to trace Peters’s amazing course across five continents, including three sojourns in the United States, which led to him being deported twice, and in doing so, established that he had continued his frauds into the 21st century. I did discover that Peters had died in 2005, and end by describing a visit to his grave, in an isolated Norfolk churchyard.

What’s your best theory as to why he persisted in his life as a con man?

Once he was on the treadmill, it was difficult to get off. Having lied so much and so often, he could not stop lying without admitting his guilt, and this would entail starting again, at the bottom of the ladder. It was easier, whenever he was rumbled (as he always was, sooner or later), to flee the scene, and start again, in another country, or another church, or school, or college.

What’s your own best guess as to what made him tick?

Everything I write about Peters is surmise. We know nothing of his inner life, or even whether he had one. I believe that he wanted adulation, and if he could not achieve the status he craved by the conventional means, he would find some other way of gaining it: awarding himself degrees, titles, qualifications, and so on.

You anticipate that some readers will believe Peters couldn’t get away with so much, so long, in the internet era. Why is that not necessarily the case?

I think that, on the contrary, it may be easier for con men to operate now, because in the modern age, people are much more reluctant to provide frank testimonials or references. Praise is acceptable, but not criticism. In a time of transparency, everything is visible, and so people hide what they truly think.