Markham swung about sharply.

“So!” he retorted. “I’m about to bedevil an innocent person, eh? Since my assistants and I are the only ones who happen to know what evidence we hold against her, perhaps you will explain by what occult process you acquired your knowledge of this person’s innocence.”

“It’s quite simple, y’ know,” Vance replied, with a quizzical twitch of the lips. “You haven’t your eye on the murderer for the reason that the person who committed this particular crime was sufficiently shrewd and perspicacious to see to it that no evidence which you or the police were likely to find, would even remotely indicate his guilt.”

He had spoken with the easy assurance of one who enunciates an obvious fact—a fact which permits of no argument.

Markham gave a disdainful laugh.

“No law-breaker,” he asserted oracularly, “is shrewd enough to see all contingencies. Even the most trivial event has so many intimately related and serrated points of contact with other events which precede and follow, that it is a known fact that every criminal—however long and carefully he may plan—leaves some loose end to his preparations, which in the end betrays him.”

“A known fact?” Vance repeated. “No, my dear fellow—merely a conventional superstition, based on the childish idea of an implacable, avenging Nemesis. I can see how this esoteric notion of the inev’tability of divine punishment would appeal to the popular imagination, like fortune-telling and Ouija boards, don’t y’ know; but—my word!—it desolates me to think that you, old chap, would give credence to such mystical moonshine.”

“Don’t let it spoil your entire day,” said Markham acridly.

“Regard the unsolved, or successful, crimes that are taking place every day,” Vance continued, disregarding the other’s irony, “—crimes which completely baffle the best detectives in the business, what? The fact is, the only crimes that are ever solved are those planned by stupid people. That’s why, whenever a man of even mod’rate sagacity decides to commit a crime, he accomplishes it with but little diff’culty, and fortified with the pos’tive assurance of his immunity to discovery.”

“Undetected crimes,” scornfully submitted Markham, “result, in the main, from official bad luck—not from superior criminal cleverness.”

“Bad luck”—Vance’s voice was almost dulcet—“is merely a defensive and self-consoling synonym for inefficiency. A man with ingenuity and brains is not harassed by bad luck. … No, Markham old dear; unsolved crimes are simply crimes which have been intelligently planned and executed. And, d’ ye see, it happens that the Benson murder falls into that categ’ry. Therefore, when, after a few hours’ investigation, you say you’re pretty sure who committed it, you must pardon me if I take issue with you.”

He paused and took a few meditative puffs on his cigarette.

“The factitious and casuistic methods of deduction you chaps pursue are apt to lead almost anywhere. In proof of which assertion I point triumphantly to the unfortunate young lady whose liberty you are now plotting to take away.”

Markham, who had been hiding his resentment behind a smile of tolerant contempt, now turned on Vance and fairly glowered.

“It so happens—and I’m speaking ex cathedra[49]—” he proclaimed defiantly, “that I come pretty near having the goods on your ‘unfortunate young lady’.”

Vance was unmoved.

“And yet, y’ know,” he observed drily, “no woman could possibly have done it.”

I could see that Markham was furious. When he spoke he almost spluttered.

“A woman couldn’t have done it, eh—no matter what the evidence?”