Merlini grinned. “I know. That was his error. Rosa is a regurgitating medium—like Helen Duncan in whose stomach the English investigator, Harry Price, found a hidden ghost—a balled-up length of cheesecloth fastened with a safety pin which showed up when he X-rayed her. X-rays of Rosa seem indicated, too. And search her hospital room and the ambulance that took her over.”

“Okay, Doran,” Gavigan ordered. “Do it.”

I saw an objection. “Now you’ve got Rosa framing herself, too,” I said. “If she swallowed the murder knife, why should she put blood on the letter opener? That makes no sense at all.”

“None of this does,” Gavigan complained.

“I know,” Merlini answered. “One knife was bad. Two are much worse. And although X-rays of Rosa before the séance would have shown shells, I predict they won’t show a knife. If they do, then Rosa needs a psychiatric examination as well.”

“Don’t worry,” Gavigan said gloomily. “She’ll get one. Her attorney will see to that. And they’ll prove she’s crazier than a bedbug without half trying. But if that knife isn’t in her. . .” His voice died.

“Then you’ll never convict her,” Merlini finished.

“If that happens,” the Inspector said ominously, “you’re going to have to explain where that knife came from, how it really disappeared, and where it is now.”

Merlini’s view was even gloomier. “It’ll be much worse than that. We’ll also have an appearing and vanishing murderer to explain—someone who entered a sealed room, killed Drake, put blood on the paper knife to incriminate Rosa, then vanished just as neatly as any of Miss Potter’s ghosts—into thin air.”

And Merlini’s prediction came true.

The X-ray plates didn’t show the slightest trace of a knife. And it wasn’t in Rosa’s hospital room or in the ambulance. Nor on Garrett, Paul, Elinor Drake, Isabelle Potter—nor, as Doran discovered, on myself. The Drake house was a mess by the time the boys got through taking it apart—but no knife with a broken point was found anywhere. And it was shown beyond doubt that there were no trapdoors or sliding panels in the study; the door and window were the only exits.

Inspector Gavigan glowered every time the phone rang—the Commissioner had already phoned twice and without mincing words expressed his dissatisfaction with the way things were going.

And Merlini, stretched out in Drake’s chair, his heels up on the desk top, his eyes closed, seemed to have gone into a trance.

“Blast it!” Gavigan said. “Rosa Rhys got that knife out of here somehow. She had to! Merlini, are you going to admit that she knows a trick or two you don’t?”