“It was a note from an artist, Thurston, who gave the address of Mrs. Boncour’s bungalow—­ah, I see you have heard of him.  He asked Dixon’s recommendation of a certain patent headache medicine.  I thought it possibly evidential, and I asked Dixon about it.  He explained it by saying that he did not have a copy of his reply, but as near as he could recall, he wrote that the compound would not cure a headache except at the expense of reducing heart action dangerously.  He says he sent no prescription.  Indeed, he thought it a scheme to extract advice without incurring the charge for an office call and answered it only because he thought Vera had become reconciled to Thurston again.  I can’t find that letter of Thurston’s.  It is gone.”

We looked at each other in amazement.

“Why, if Dixon contemplated anything against Miss Lytton, should he preserve this letter from her?” mused Kennedy.  “Why didn’t he destroy it?”

“That’s what puzzles me,” remarked Leland.  “Do you suppose some one has broken in and substituted this Lytton letter for the Thurston letter?”

Kennedy was scrutinising the letter, saying nothing.  “I may keep it?” he asked at length.  Leland was quite willing and even undertook to obtain some specimens of the writing of Vera Lytton.  With these and the letter Kennedy was working far into the night and long after I had passed into a land troubled with many wild dreams of deadly poisons and secret intrigues of artists.

The next morning a message from our old friend First Deputy O’Connor in New York told briefly of locating the rooms of an artist named Thurston in one of the co-operative studio apartments.  Thurston himself had not been there for several days and was reported to have gone to Maine to sketch.  He had had a number of debts, but before he left they had all been paid—­ strange to say, by a notorious firm of shyster lawyers, Kerr & Kimmel.  Kennedy wired back to find out the facts from Kerr & Kimmel and to locate Thurston at any cost.

Even the discovery of the new letter did not shake the wonderful self-possession of Dr. Dixon.  He denied ever having received it and repeated his story of a letter from Thurston to which he had replied by sending an answer, care of Mrs. Boncour, as requested.  He insisted that the engagement between Miss Lytton and himself had been broken before the announcement of his engagement with Miss Willard.  As for Thurston, he said the man was little more than a name to him.  He had known perfectly all the circumstances of the divorce, but had had no dealings with Thurston and no fear of him.  Again and again he denied ever receiving the letter from Vera Lytton.