"Yes?" Cavender asked.
Perrie glanced at Dexter Jones, at Mavis.
"But then what did happen?" she asked bewilderedly, of the other two as much as of Cavender. "Mr. Cavender, I saw something appear on that plate! I know it did. It was a sandwich. It looked perfectly natural. I don't think it could have possibly been something Mr. Grady did with mirrors. And how could it have had the paper napkin Mavis had just been thinking about wrapped around it, unless...."
"Unless it actually was a materialization of a mental image you'd created between you?" Cavender said. "Now settle back and relax, Perrie. There's a more reasonable explanation for what happened tonight than that."
He waited a moment, went on. "Grady's one real interest is money and since none of you have any to speak of, his interest in you was that you could help him get it. Perrie and Dexter showed some genuine talent to start with, in the line of guessing what card somebody was thinking about and the like. It's not too unusual an ability, and in itself it wasn't too useful to Grady.
"But he worked on your interest in the subject. All the other students, the paying students, had to lose was a sizable amount of cash ... with the exception of Mrs. Folsom who's been the next thing to a flip for years anyway. She was in danger. And you three stood a good chance of letting Grady wreck your lives. I said he's a competent hypnotist. He is. Also a completely ruthless one."
He looked at Mavis. "As far as I know, Mavis, you haven't ever demonstrated that you have any interesting extrasensory talents like Dexter's and Perrie's. Rather the contrary. Right?"
She nodded, her eyes huge.
"I've always tested negative. Way down negative. That's why I was really rather shocked when that.... Of course, I've always been fascinated by such things. And he insisted it would show up in me sometime."
"And," Cavender said, "several times a week you had special little training sessions with him, just as his two star pupils here did, to help it show up. You were another perfect stooge, from Grady's point of view. Well, what it amounts to is that Grady was preparing to make his big final killing off this group before he disappeared from the city. He would have collected close to thirty thousand dollars tonight, and probably twice as much again within the next month or so before any of the students began to suspect seriously that Dr. Al's instruments could be the meaningless contraptions they are.