"None. The office has been locked, and there is no evidence of any one
having entered or disturbed a thing."

He was hastily running over the pile of letters as if looking to see
whether they were all there. Suddenly he stopped.

"Yes," he exclaimed excitedly, "one of them _is_ gone." Nervously he
fumbled through them again. "One is gone," he repeated, looking at us,
startled.

"What was is about?" asked Craig.

"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?"