Gavigan was apparently remembering Merlini’s demonstration with the gun in his office. “If you,” he warned acidly, “so much as try to hint that one of the people outside this room projected some mental force that knocked Rosa out and then caused the knife to stab Drake—”

“You know,” Merlini said, “I half expected Miss Potter would suggest that. But her theory is even more disturbing.” He looked at me. “She says that the benign spirits which Rosa usually evoked were overcome by some malign and evil entity whose astral substance materialized momentarily, killed Drake, then returned to the other world from which it came.”

“She’s a mental case, too,” Gavigan said disgustedly. “They have to be crazy if they expect anyone to believe any such—”

“That,” Merlini said quietly, “may be another reason Rosa is scared to death. Perhaps she believes it but knows you won’t. In her shoes, I’d be scared, too.” He frowned. “The difficulty is the knife.”

Gavigan blinked. “The knife? What’s difficult about that?”

“If I killed Drake,” Merlini replied, “and wanted appearances to suggest that psychic forces were responsible, you wouldn’t have found a weapon in this room that made it look as if I were guilty. I would have done a little de-apporting and made it disappear. As it is now, even if the knife was propelled supernaturally, Rosa takes the rap.”

“And how,” Gavigan demanded, “would you make the knife disappear if you were dressed, as she was, in practically nothing?” With sudden suspicion, he added, “Are you suggesting that there’s a way she could have done that—and that you think she’s not guilty because she didn’t?”

Merlini lifted one of the shells from the table and placed it in the center of his left palm. His right hand covered it for a brief moment, then moved away. The shell was no longer there; it had vanished as silently and as easily as a ghost. Merlini turned both hands palms outward; both were unmistakably empty.

“Yes,” he said, “she could have made the knife disappear—if she had wanted to. The same way she produced the two shells.”

He made a reaching gesture with his right hand and the missing shell reappeared suddenly at his fingertips.

Gavigan looked annoyed and relieved at the same time. “So,” he said, “you do know how she got those shells in here. I want to hear it. Right now.”

But Gavigan had to wait.

At that moment a torpedo hit the water-tight circumstantial case against Rosa Rhys and detonated with a roar.

Doran, who had answered the phone a moment before, was swearing profusely. He was staring at the receiver he held as though it were a live cobra he had picked up by mistake.