"Be careful in answering my questions," warned The Thinking Machine when Grayson answered. "Do you know how long Miss Winthrop has owned the little silver box which is now on her desk, near the telephone?"
Grayson glanced round involuntarily to where the girl sat idly turning over the leaves of her book. "Yes," he answered, "for seven months. I gave it to her last Christmas."
"Ah!" exclaimed the scientist. "That simplifies matters. Where did you buy it?"
Grayson mentioned the name of a well-known jeweler.
Considerably later in the day The Thinking Machine called Grayson to the telephone again.
"What make of typewriter does she use?" came the querulous voice over the wire.
Grayson named it.
While Grayson sat with deeply perplexed lines in his face, the diminutive scientist called upon Hutchinson Hatch at his office.
"Do you use a typewriter?" demanded The Thinking Machine.
"Yes."