Ballinger still appeared puzzled. Monk looked at his hands on the leather inlaid surface of the desk. They were motionless, deliberately held still.

Monk smiled. “I have an idea as to the time you crossed the river, by ferry …” He saw a very faint smile lift the corners of Ballinger’s mouth, and in that instant Monk knew that in spite of Ballinger’s affectation to the contrary, he was not surprised. “Naturally, we questioned anyone that we knew would be in the area,” Monk went on almost expressionlessly. “Such as ferrymen. It is always possible that any witness might have seen something that would later have meaning for them.”

“I did not see Rupert Cardew,” Ballinger replied, studying Monk’s face. “At least not so far as I know. I observed a few other people on the river; some of them looked to be young men, no doubt about private pleasures. I could not responsibly identify any of them. I’m sorry.”

“Even so,” Monk persisted. “If you could tell me the time, as closely as you know it, and exactly what you did see, it might help.”

Ballinger hesitated, as if still puzzled as to its importance.

“Even if it merely confirms someone else’s story,” Monk added. “Or proves it false.”

“I couldn’t identify anyone,” Ballinger said, and gave a slight gesture of helplessness. “Apart from the ferryman, of course, Stanley Willington.”

“Of course,” Monk agreed. “But if you saw one person, or two, it could help. Or if you saw no one, at a time someone claimed to be there …” He allowed it to hang in the air, self-explanatory.

“Yes … I see. Let me think.” Ballinger’s eyes never left Monk’s, as if it were a kind of duel to which neither of them would admit. “I took a hansom as far as Chiswick. I think I arrived there about nine. There were still a number of people around, although it was dark. I saw them as figures on the quayside, talking, laughing. I smelled smoke—cigars. I recall that. It is a highly recognizable aroma. And it suggests gentlemen.”

Monk nodded. It was a clever observation, and he acknowledged it.

“I waited about ten minutes for a ferry. I preferred to have Stanley. He entertains me.” The description was good, and it matched Willington’s own account, as no doubt Ballinger knew it would.

Ballinger continued. All of it was in accordance with what Monk already knew, but it served the purpose he intended. He would check on it, not only with the men on the river, all the way up to Mortlake, a distance of nearly a mile and a half, but with Bertie Harkness, whose address Ballinger also offered.

“Thank you,” Monk said when he was finished and standing by the door. “It may help us catch someone in a lie.”