“The note you saw him remove from the dog’s collar,” Ellery said. “It was on thin paper, didn’t you tell me?”
“Very. A sort of flimsy, or onionskin.”
“White?”
“White.”
Ellery nodded. He went over to the exposed mattress. “He was in this room for a week, Laurel, between his attack and death. During that week did he have many visitors?”
“The Priam household. Some people from the office. A few friends.”
“Some time during that week,” said Ellery, “your father decided that the note he had received was in danger of being stolen or destroyed. So he took out insurance.” His finger traced on the side wall of the mattress one of the perpendicular blue lines of the ticking. “He had no tool but a dull penknife from the night table there. And I suppose he was in a hurry, afraid he might be caught at it. So the job had to be crude.” Half his finger suddenly vanished. “He simply made a slit here, where the blue line meets the undyed ticking. And he slipped the paper into it, where I found it.”
“The note,” breathed Laurel. “You’ve found the note. Let me see!”
Ellery put his hand in his pocket. But just as he was about to withdraw it, he stopped. His eyes were on one of the windows.
Some ten yards away there was an old walnut tree.