Sachs started toward the window.

“No,” Rhyme said to her. “We still don’t know for certain he’s gone.” Sellitto stood away from the glass as he drew the drapes shut.

Oddly, it was scarier not knowing exactly where the Dancer was than thinking he was pointing a large rifle through a window twenty feet away.

It was then that Cooper’s phone rang. He took the call.

“Lincoln, it’s the Bureau’s bomb people. They’ve checked the Explosives Reference Collection. They say they’ve got a possible match on those bits of latex.”

“What do they say?”

Cooper listened to the agent for a moment.

“No leads on the specific type of rubber, but they say it’s not inconsistent with a material used in altimeter detonators. There’s a latex balloon filled with air. It expands when the plane goes up because of the low pressure at higher altitudes, and at a certain height the balloon presses into a switch on the side of the bomb wall. Contact’s completed. The bomb goes off.”

“But this bomb was detonated by a timer.”

“They’re just telling me about the latex.”

Rhyme looked at the plastic bags containing components of the bomb. His eyes fell to the timer, and he thought: Why’s it in such perfect shape?

Because it had been mounted behind the overhanging lip of steel.

But the Dancer could have mounted it anywhere, pressed it into the plastic explosive itself, which would have reduced it to microscopic pieces. Leaving the timer intact had seemed careless at first. But now he wondered.

“Tell him that the plane exploded as it was descending,” Sachs said.

Cooper relayed the comment, then listened. The tech reported, “He says it could just be a point-of-construction variation. As the plane climbs, the expanding balloon trips a switch that arms the bomb; when the plane descends the balloon shrinks and closes the circuit. That detonates it.”

Rhyme whispered, “The timer’s a fake! He mounted it behind the piece of metal so it wouldn’t be destroyed. So we’d think it was a time bomb, not an altitude bomb. How high was Carney’s plane when it exploded?”

Sellitto raced through the report. “It was just descending through five thousand feet.”

“So it armed when they climbed through five thousand outside of Mamaroneck and detonated when he went below it near Chicago,” Rhyme said.

“Why on descent?” the detective asked.

“So the plane would be farther away?” Sachs suggested.

“Right,” Rhyme said. “It’d give the Dancer a better chance to get away from the airport before it blew.”

“But,” Cooper asked, “why go to all the trouble to fool us into thinking it was one kind of bomb and not another?”

Rhyme saw that Sachs figured it out just as fast as he did. “Oh, no!” she cried.

Sellitto still didn’t get it. “What?”

“Because,” she said, “the bomb squad was looking for a time bomb when they searched Percey’s plane tonight. Listening for the timer.”

“Which means,” Rhyme spat out, “Percey and Bell ’ve got an altitude bomb on board too.”

“Sink rate twelve hundred feet per minute,” Brad sang out.

Percey gentled the yoke of the Lear back slightly, slowing the descent. They passed through fifty-five hundred feet.

Then she heard it.

A strange chirping sound. She’d never heard any sound like it, not in a Lear 35A. It sounded like a warning buzzer of some kind, but distant. Percey scanned the panels but could see no red lights. It chirped again.

“Five three hundred feet,” Brad called. “What’s that noise?”

It stopped abruptly.

Percey shrugged.

An instant later, she heard a voice shouting beside her, “Pull up! Go higher! Now!”

Roland Bell’s hot breath was on her cheek. He was beside her, in a crouch, brandishing his cell phone.

“What?”

“There’s a bomb on! Altitude bomb. It goes off when we hit five thousand feet.”

“But we’re above -”

“I know! Pull up! Up!”

Percey shouted, “Set power, ninety-eight percent. Call out altitude.”

Without a second’s hesitation, Brad shoved the throttles forward. Percey pulled the Lear into a ten-degree rotation. Bell stumbled backward and landed with a crash on the floor.

Brad said, “Five thousand two, five one five… five two, five thousand three, five four… five eight. Six thousand feet.”

Percey Clay had never declared an emergency in all her years flying. Once, she’d declared a “pan-pan” – indicating an urgency situation – when an unfortunate flock of pelicans decided to commit suicide in her number two engine and clog up her pitot tube to boot. But now, for the first time in her career, she said, “May-day, may-day, Lear Six Niner Five Foxtrot Bravo.”

“Go ahead, Foxtrot Bravo.”

“Be advised, Chicago Approach. We have reports of a bomb on board. Need immediate clearance to one zero thousand feet and a heading for holding pattern over unpopulated area.”

“Roger, Niner Five Foxtrot Bravo,” the ATC controller said calmly. “Uhm, maintain present heading of two four zero. Cleared to ten thousand feet. We are vectoring all aircraft around you… Change transponder code to seven seven zero zero and squawk.”

Brad glanced uneasily at Percey as he changed the transponder setting – to the code that automatically sent a warning signal to all radar facilities in the area that Foxtrot Bravo was in trouble. Squawking meant sending out a signal from the transponder to let everyone at ATC and other aircraft know exactly which blip was the Lear.

She heard Bell say into his phone, “Th’only person got close to the plane, ’cept for me and Percey, was the business manager, Ron Talbot – and, nothing personal to him, but my boys or I watched him like a hawk while he was doing the work, stood over his shoulder the whole time. Oh, and that guy delivered some of the engine parts came by too. From Northeast Aircraft Distributors in Greenwich. But I checked him out good. Even got his home phone and called his wife, had them talk – to make sure he was legit.” Bell listened for a moment more then hung up. “They’ll call us back.”

Percey looked at Brad and at Bell, then returned to the task of piloting her aircraft.

“Fuel?” she asked her copilot. “How much time?”

“We’re under our estimated. Headwinds’ve been good.” He did the calculations. “A hundred and five minutes.”

She thanked God, or fate, or her own intuition, for deciding not to refuel at Chicago, but to load enough to get them to Saint Louis, plus the FAA requirement for an additional forty-five minutes’ flying time.

Bell’s phone chirped again.

He listened, sighed, then asked Percey, “Did that Northeast company deliver a fire extinguisher cartridge?”

“Shit, did he put it in there?” she asked bitterly.

“Looks like it. The delivery truck had a flat tire just after it left the warehouse on the way to make that delivery to you. Driver was busy for about twenty minutes. Connecticut trooper just found a mess of what looks like carbon dioxide foam in the bushes right near where it happened.”

“God damn!”Percey glanced involuntarily toward the engine. “And I installed the fucker myself.”

Bell asked, “Rhyme wants to know about heat. Wouldn’t it blow the bomb?”

“Some parts are hot, some aren’t. It’s not that hot by the cartridge.”

Bell told this to Rhyme, then he said, “He’s going to call you directly.”

A moment later, through the radio, Percey heard the patch of a unicom call.

It was Lincoln Rhyme.

“Percey, can you hear me?”

“Loud and clear. That prick pulled a fast one, hm?”

“Looks like it. How much flying time do you have?”

“Hour forty-five minutes. About.”

“Okay, okay,” the criminalist said. A pause. “All right… Can you get to the engine from the inside?”

“No.”

Another pause. “Could you somehow disconnect the whole engine? Unbolt it or something? Let it drop off?”