“Don’t trust your gut,” I recounted from memory, “trust the evidence. Don’t trust your instinct—trust the context. Don’t trust your experience—trust the facts.”

He smiled. “Either you’re a good student or I’m a good teacher.”

“Let’s go with you being a good teacher.”

Calvin rubbed his thumb fondly along the book’s spine. “Vidocq was quite a raconteur. For instance . . .” He flipped through the pages, muttering to himself. “Let’s see if I can find an example . . .” Then he paused. “Ah. Yes. Here. Page thirty-one: ‘I spare details, but it is sufficient to say that I was arrested dressed in women’s clothes as I was fleeing from the wrath of a jealous husband.’ Now that’s a great line.”

“That is a great line.”

“Yes, and regarding his investigative approach, he blazed new trails in working undercover, which is what got me thinking of him in the first place when you were telling me about the case.”

“About the Matchmaker?”

“Yes.”

Calvin still hadn’t told me if he’d heard of the Matchmaker before, but I trusted that this discussion of Vidocq’s techniques was not a rabbit trail.

“How, specifically, was Vidocq a pioneer in undercover work?” I asked.

“In ways that today might seem self-evident but weren’t typically practiced by law enforcement in those days: Change your name; go where the criminals are; disguise yourself, your posture, your voice, your appearance.”

“Makes sense.”

“Yes. And it’s best to go in alone. The more people you try to take into a den of thieves, the more things may go wrong. And when that happens, it puts everyone in more danger and jeopardizes the investigation.”

Although we typically strive for overwhelming force when we confront suspects, undercover work was different.

“That makes sense too,” I said.

“Regarding the forensic aspects of a case, Vidocq analyzed pieces of clothing and bits of paper for trace evidence and studied sole impressions in mud to deduce who committed a crime. He even noted that those who serve time and return to their life of crime do so ‘with all the advantages of prison experience.’”

“All too often, prison serves as an advanced class in how to get away with murder.”

“Precisely. Also, he noted that the guilty tend to fall into one of two extremes—they become either quiet or overly talkative. Or, as he put it, they exhibit ‘a dreary silence or an unendurable volubility.’”

“I need to read Vidocq.”

He passed the book to me. “And that is why I purchased it for you.”

“Really, Calvin, you don’t need to do that. I can pay you for—”

He emphatically waved off my offer. “His memoir is undoubtedly a mixture of fact and myth, and it’s somewhat difficult to discern at what points he’s recounting history and at what points he’s embellishing it in his favor. Nevertheless, it is worth a read.”