“The Doctor?”
Miss Cornelia knitted on as if every movement of her needles added one more link to the strong chain of probabilities she was piecing together.
“When Doctor Wells said he was leaving here earlier in the evening for the Johnsons’ he did not go there,” she observed. “He was not expected to go there. I found that out when I telephoned.”
“The Doctor!” repeated the detective, his eyes narrowing, his head beginning to sway from side to side like the head of some great cat just before a spring.
“As you know,” Miss Cornelia went on, “I had a supplementary bolt placed on that terrace door today.” She nodded toward the door that gave access into the alcove from the terrace. “Earlier this evening Doctor Wells said that he had bolted it, when he had left it open—purposely, as I now realize, in order that he might return later. You may also recall that Doctor Wells took a scrap of paper from Richard Fleming’s hand and tried to conceal it—why did he do that?”
She paused for a second. Then she changed her tone a little.
“May I ask you to look at this?”
She displayed the piece of paper on which Doctor Wells had started to write the prescription for her sleeping-powders—and now her strategy with the doctor’s bag and the soot Jack Bailey had got from the fireplace stood revealed. A sharp, black imprint of a man’s right thumb—the Doctor’s—stood out on the paper below the broken line of writing. The Doctor had not noticed the staining of his hand by the blackened bag handle, or, noticing, had thought nothing of it—but the blackened bag handle had been a trap, and he had left an indelible piece of evidence behind him. It now remained to test the value of this evidence.
Miss Cornelia handed the paper to Anderson silently. But her eyes were bright with pardonable vanity at the success of her little piece of strategy.
“A thumb-print,” muttered Anderson. “Whose is it?”