I stared into the chest and did not answer.
"It looks like another way into this room, doesn't it"--and then he started--"or out of it. I hadn't thought of that. Wait."
He took an old envelope from his pocket, dropped it into the chest, and locked it. He waited a moment, then opened the chest again. The envelope had gone.
"I confess, Wigan, that this is a surprise," said Quarles. "I must go home and think. I believe--yes, I believe we have the clew. You must search Portman's papers for some reference to a business acquaintance, probably a foreigner. Perhaps Portman knows Italy--Florence. It might very likely be Florence. I fancy this chest had its home there. If you find any reference to a friend who is a Florentine, and can lay hands on him, you might question him closely about his movements on the day of Portman's disappearance."
"The first thing is to get this chest moved," I said.
"Let that wait for forty-eight hours," said Quarles. "We may have a more complete story by then. Give me until to-morrow night, then come and see me."
When I went to Chelsea the following night I was taken at once to the empty room. Zena was there. Quarles was standing by his table, on which was a rough plan, evidently a production of his own, and quite unintelligible without an explanation.
"Of course you have not discovered anything yet, Wigan?"
"No, quite so," he said, motioning me to a seat. "But we have a fairly clear story, I think. Zena said, you remember, that she would like to know something about the man who was coming to dine with Portman that night. It was an important point, particularly so since the guest did not put in an appearance. You saw the importance of it, Wigan, because you asked Isaacson whether he was the expected guest. Now, Isaacson had seen Portman after he had left his house that night, but had not spoken to him. This fact suggested a question to my mind: was Isaacson telling the truth? There were two possibilities. Isaacson might have seen him, gone with him, and be responsible for his disappearance; or he might have been mistaken. The man he saw might not have been Portman. The second possibility was the one which appealed to me. The fact remained, however, that Isaacson knew him well, therefore the man he took to be Portman must have wished to be taken for Portman, I argued. This would account for his hurrying on without speaking, since a closer investigation might have betrayed him. I looked for some fact to support this theory. I found it in Isaacson's statement that Portman wore glasses in the street on this occasion, which was unusual, so unusual, mark you, that Isaacson noticed it. Now, if my theory were right, it seemed possible that after Mr. Portman entered his room that afternoon he never left it. That he was there when Mrs. Eccles took in the tea-tray there could be no doubt; but that it was Mr. Portman who answered through the locked door was another matter.