The Mammoth Book of Locked-Room Mysteries And Impossible Crimes

got started.”

“How’s it work?”

“It displaces the oxygen in the room,” I said. “I’m not enough of a scientist to know how it manages it, but the net effect is about the same as that great speckled bird you were talking about. The one with the pillows.”

“That’d be consistent with the physical evidence,” Crittenden said. “But how would you get this Halon in here?”

“It was already here,” I said. I pointed to the jets on the walls and ceiling. “When I first saw them, I thought Bellermann had put in a conventional sprinkler system, and I couldn’t believe it. Water’s harder than fire on rare books, and a lot of libraries have been totalled when a sprinkler system went off by accident. I said something to that effect to Karl, and he just about bit my head off, making it clear he wouldn’t expose his precious treasures to water damage.

“So I got the picture. The jets were designed to deliver gas, not liquid, and it went without saying that the gas would be Halon. I understand they’re equipping the better research libraries with it these days, although Karl’s the only person I know of who installed it in his personal library.”

Crittenden was halfway up a ladder, having a look at one of the outlets. “Just like a sprinkler head,” he said, “which is what I took it for. How’s it know when to go off? Heat sensor?”

“That’s right.”

“You said murder. That’d mean somebody set it off.”

“Yes.”

“By starting a fire in here? Be a neater trick than sending in the great speckled bird.”

“All you’d have to do,” I said, “is heat the sensor enough to trigger the response.”

“How?”

“When I was in here earlier,” I said, “I caught a whiff of smoke. It was faint, but it was absolutely there. I think that’s what made me ask Karl about fire in the first place.”

“And?”

“When Mrs Bellermann and I came in and discovered the body, the smell was gone. But there was a discoloured spot on the carpet that I’d noticed before, and I bent down for a closer look at it.” I pointed to the Tabriz (which, now that I think about it, may very well have been an Isfahan). “Right there,” I said.

Crittenden knelt where I pointed, rubbed two fingers on the spot, brought them to his nose. “Scorched,” he reported. “But just the least bit. Take a whole lot more than that to set off a sensor way up there.”

“I know. That was a test.”

“A test?”

“Of the murder method. How do you raise the temperature of a room you can’t enter? You can’t unlock the door and you can’t open the window. How can you get enough heat in to set off the gas?”

“How?”

I turned to Eva. “Tell him how you did it,” I said.

“I don’t know what you’re talking about,” she said. “You must be crazy.”

“You wouldn’t need a fire,” I said. “You wouldn’t even need a whole lot of heat. All you’d have to do is deliver enough heat directly to the sensor to trigger a response. If you could manage that in a highly localized fashion, you wouldn’t even raise the overall room temperature appreciably.”

“Keep talking,” Crittenden said.

I picked up an ivory-handled magnifier, one of several placed strategically around the room. “When I was a Boy Scout,” I said, “they didn’t really teach me how to open locks. But they were big on starting fires. Flint and steel, fire by friction – and that old standby, focusing the sun’s rays though a magnifying glass and delivering a concentrated pinpoint of intense heat onto something with a low kindling point.”

“The window,” Crittenden said.

I nodded. “It faces north,” I said, “so the sun never comes in on its own. But you can stand a few feet from the window and catch the sunlight with a mirror, and you can tilt the mirror so the light is reflected through your magnifying glass and on through the window. And you can beam it onto an object in the room.”

“The heat sensor, that’d be.”

“Eventually,” I said. “First, though, you’d want to make sure it would work. You couldn’t try it out ahead of time on the sensor, because you wouldn’t know it was working until you set it off. Until then, you couldn’t be sure the thickness of the window glass wasn’t disrupting the process. So you’d want to test it.”

“That explains the scorched rug, doesn’t it?” Crittenden stooped for another look at it, then glanced up at the window. “Soon as you saw a wisp of smoke or a trace of scorching, you’d know it was working. And you’d have an idea how long it would take to raise the temperature enough. If you could make it hot enough to scorch wool, you could set off a heat-sensitive alarm.”

“My God,” Eva cried, adjusting quickly to new realities. “I thought you must be crazy, but now I can see how it was done. But who could have done such a thing?”

“Oh, I don’t know,” I said. “I suppose it would have to be somebody who lived here, somebody who was familiar with the library and knew about the Halon, somebody who stood to gain financially by Karl Bellermann’s death. Somebody, say, who felt neglected by a husband who treated her like a housekeeper, somebody who might see poetic justice in killing him while he was locked away with his precious books.”

“You can’t mean me, Bernie.”

“Well, now that you mention it…”

“But I was with you! Karl was with us at lunch. Then he went into the library and I showed you to the guest room.”

“You showed me, all right.”

“And we were together,” she said, lowering her eyes modestly. “It shames me to say it with my husband tragically dead, but we were in bed together until almost six o’clock, when we came down here to discover the body. You can testify to that, can’t you, Bernie?”

“I can swear we went to bed together,” I said, “And I can swear that I was there until six, unless I went sleepwalking. But I was out cold, Eva.”

“So was I.”

“I don’t think so,” I said. “You stayed away from the coffee, saying how it kept you awake. Well, it sure didn’t keep me awake. I think there was something in it to make me sleep, and that’s why you didn’t want any. I think there was more of the same in the pot you gave Karl to bring in here with him, so he’d be dozing peacefully while you set off the Halon. You waited until I was asleep, went outside with a mirror and a magnifier, heated the sensor and set off the gas, and then came back to bed. The Halon would do its work in minutes, and without warning even if Karl wasn’t sleeping all that soundly. Halon’s odourless and colourless, and the air cleaning system would whisk it all away in less than an hour. But I think there’ll be traces in his system, along with traces of the same sedative they’ll find in the residue in both the coffee pots. And I think that’ll be enough to put you away.”

Crittenden thought so, too.

When I got back to the city there was a message on the machine to call Nizar Gulbenkian. It was late, but it sounded urgent.

“Bad news,” I told him. “I had the book just about sold. Then he locked himself in his library to commune with the ghosts of Rex Stout and Franklin Delano Roosevelt, and next thing he knew they were all hanging out together.”

“You don’t mean he died?”