“I’m quite convinced, y’ know, that you won’t believe me,” he returned, in an even, matter-of-fact voice. “But it was Spotswoode who killed the girl.”

“You don’t tell me!” Markham spoke with undisguised irony. “So it was Spotswoode! My dear Vance, you positively bowl me over. I would telephone Heath at once to polish up his handcuffs, but, unfortunately, miracles—such as strangling persons from across town—are not recognized possibilities in this day and age. . . . Do let me order you another croissant.”

Vance extended his hands in a theatrical gesture of exasperated despair.

“For an educated, civilized man, Markham, there’s something downright primitive about the way you cling to optical illusions. I say, y’ know, you’re exactly like an infant who really believes that the magician generates a rabbit in a silk hat, simply because he sees it done.”

“Now you’re becoming insulting.”

“Rather!” Vance pleasantly agreed. “But something drastic must be done to disentangle you from the Lorelei of legal facts. You’re so deficient in imagination, old thing.”

“I take it that you would have me close my eyes and picture Spotswoode sitting up-stairs here in the Stuyvesant Club and extending his arms to 71st Street. But I simply couldn’t do it. I’m a commonplace chap. Such a vision would strike me as ludicrous; it would smack of a hasheesh dream. . . . You yourself don’t use Cannabis indica, do you?”

“Put that way, the idea does sound a bit supernatural. And yet: Certum est quia impossibile est. I rather like that maxim, don’t y’ know; for, in the present case, the impossible is true. Oh, Spotswoode’s guilty—no doubt about it. And I’m going to cling tenaciously to that apparent hallucination. Moreover, I’m going to try to lure you into its toils; for your own—as we absurdly say—good name is at stake. As it happens, Markham, you are at this moment shielding the real murderer from publicity.”

Vance had spoken with the easy assurance that precludes argument; and from the altered expression on Markham’s face I could see he was moved.

“Tell me,” he said, “how you arrived at your fantastic belief in Spotswoode’s guilt.”