Everyone looked up at the newly arranged, single line of text onthe wall-screen.

"Still garbage," Jabba scoffed in disgust. "Lookat it. It's totally random bits of-" The wordslodged in his throat. His eyes widened to saucers. "Oh ...oh my ..."

Fontaine had seen it too. He arched his eyebrows, obviouslyimpressed.

Midge and Brinkerhoff both cooed in unison. "Holy ...s.h.i.t."

The sixty-four letters now read: PRIMEDIFFERENCEBETWEENELEMENTSRESPONSIBLEFORHIROSHIMAA NDNAGASAKI "Put in the s.p.a.ces," Susan ordered. "We'vegot a puzzle to solve."

CHAPTER 123

An ashen technician ran to the podium. "Tunnel block'sabout to go!"

Jabba turned to the VR onscreen. The attackers surged forward,only a whisker away from their a.s.sault on the fifth and final wall.The databank was running out of time.

Susan blocked out the chaos around her. She read Tankado'sbizarre message over and over.

PRIME DIFFERENCE BETWEEN ELEMENTS RESPONSIBLE FORHIROSHIMA AND NAGASAKI "It's not even a question!" Brinkerhoff cried."How can it have an answer?"

"We need a number," Jabba reminded. "Thekill-code is numeric."

"Silence," Fontaine said evenly. He turned andaddressed Susan. "Ms. Fletcher, you've gotten us thisfar. I need your best guess."

Susan took a deep breath. "The kill-code entry fieldaccepts numerics only. My guess is that this is some sort ofclue as to the correct number. The text mentions Hiroshima andNagasaki-the two cities that were hit by atomic bombs. Maybethe kill-code is related to the number of casualties, the estimateddollars of damage ..." She paused a moment, rereading theclue. "The word 'difference' seems important. Theprime difference between Nagasaki and Hiroshima. ApparentlyTankado felt the two incidents differed somehow."

Fontaine's expression did not change. Nonetheless, hope wasfading fast. It seemed the political backdrops surrounding the twomost devastating blasts in history needed to be a.n.a.lyzed, compared,and translated into some magic number ... and all within the nextfive minutes.

CHAPTER 124

"Final shield under attack!"

On the VR, the PEM authorization programming was now beingconsumed. Black, penetrating lines engulfed the final protectiveshield and began forcing their way toward its core.

Prowling hackers were now appearing from all over the world. Thenumber was doubling almost every minute. Before long, anyone with acomputer-foreign spies, radicals, terrorists-would haveaccess to all of the U.S. government's cla.s.sifiedinformation.

As technicians tried vainly to sever power, the a.s.sembly on thepodium studied the message. Even David and the two NSA agents weretrying to crack the code from their van in Spain.

PRIME DIFFERENCE BETWEEN ELEMENTS RESPONSIBLE FORHIROSHIMA AND NAGASAKI Soshi thought aloud. "The elements responsible forHiroshima and Nagasaki ... Pearl Harbor? Hirohito's refusalto ..."

"We need a number," Jabba repeated, "notpolitical theories. We're talking mathematics-nothistory!"

Soshi fell silent.

"How about payloads?" Brinkerhoff offered."Casualties? Dollars damage?"

"We're looking for an exact figure," Susanreminded. "Damage estimates vary." She stared up at themessage. "The elements responsible ..."

Three thousand miles away, David Becker's eyes flew open."Elements!" he declared.

"We're talking math,not history!"

All heads turned toward the satellite screen.

"Tankado's playing word games!" Becker spouted."The word 'elements' has multiplemeanings!"

"Spit it out, Mr. Becker," Fontaine snapped.

"He's talking about chemical elements-notsociopolitical ones!" Becker's announcement met blank looks.

"Elements!" he prompted. "The periodic table! Chemical elements! Didn't any of you see the movie FatMan and Little Boy-about the Manhattan Project? The twoatomic bombs were different. They used differentfuel-different elements!"

Soshi clapped her hands. "Yes! He's right! I readthat! The two bombs used different fuels! One used uranium and oneused plutonium! Two different elements!"

A hush swept across the room.

"Uranium and plutonium!" Jabba exclaimed, suddenlyhopeful. "The clue asks for the difference between thetwo elements!" He spun to his army of workers. "Thedifference between uranium and plutonium! Who knows what itis?"

Blank stares all around.

"Come on!" Jabba said. "Didn't you kids goto college? Somebody! Anybody! I need the difference betweenplutonium and uranium!"

No response.

Susan turned to Soshi. "I need access to the Web. Is therea browser here?"

Soshi nodded. "Netscape's sweetest."

Susan grabbed her hand. "Come on. We're goingsurfing."

CHAPTER 125

"How much time?" Jabba demanded from the podium.

There was no response from the technicians in the back. Theystood riveted, staring up at the VR. The final shield was gettingdangerously thin.

Nearby, Susan and Soshi pored over the results of theirWebsearch. "Outlaw Labs?"

Susan asked. "Who arethey?"

Soshi shrugged. "You want me to open it?" "d.a.m.n right," she said. "Six hundred forty-seventext references to uranium, plutonium, and atomic bombs. Soundslike our best bet."

Soshi opened the link. A disclaimer appeared.

The information contained in this file is strictly foracademic use only. Any layperson attempting to construct any of thedevices described runs the risk of radiation poisoning and/orself-explosion.

"Self-explosion?" Soshi said. "Jesus."

"Search it," Fontaine snapped over his shoulder."Let's see what we've got."

Soshi plowed into the doc.u.ment. She scrolled past a recipe forurea nitrate, an explosive ten times more powerful than dynamite.The information rolled by like a recipe for b.u.t.terscotchbrownies.

"Plutonium and uranium," Jabba repeated."Let's focus."

"Go back," Susan ordered. "The doc.u.ment'stoo big. Find the table of contents."

Soshi scrolled backward until she found it.

I. Mechanism of an Atomic Bomb A) Altimeter B) Air Pressure Detonator C) Detonating Heads D) Explosive Charges E) Neutron Deflector F) Uranium & Plutonium G) Lead Shield H) Fuses II. Nuclear Fission/Nuclear Fusion A) Fission (A-Bomb) & Fusion (H-Bomb) B) U-235, U-238, and Plutonium III. History of the Atomic Weapons A) Development (The Manhattan Project) B) Detonation 1) Hiroshima 2) Nagasaki 3) By-products of Atomic Detonations 4) Blast Zones "Section two!" Susan cried. "Uranium andplutonium! Go!"

Everyone waited while Soshi found the right section. "Thisis it," she said. "Hold on."

She quickly scanned thedata. "There's a lot of information here. A whole chart.How do we know which difference we're looking for? One occursnaturally, one is man- made. Plutonium was first discoveredby-"

"A number," Jabba reminded. "We need a number."

Susan reread Tankado's message. The prime differencebetween the elements ... the difference between ... we need anumber ... "Wait!" she said. "The word'difference'

has multiple meanings. We need a number-so we're talking math. It'sanother of Tankado's word games-'difference'means subtraction."

"Yes!" Becker agreed from the screen overhead."Maybe the elements have different numbers of protons orsomething? If you subtract-"

"He's right!" Jabba said, turning to Soshi."Are there any numbers on that chart?

Proton counts?Half-lives? Anything we can subtract?"

"Three minutes!" a technician called.

"How about supercritical ma.s.s?" Soshi ventured."It says the supercritical ma.s.s for plutonium is 35.2pounds."

"Yes!" Jabba said. "Check uranium! What'sthe supercritical ma.s.s of uranium?"

Soshi searched. "Um ... 110 pounds."

"One hundred ten?" Jabba looked suddenly hopeful."What's 35.2 from 110?"

"Seventy-four point eight," Susan snapped. "But Idon't think-"

"Out of my way," Jabba commanded, plowing toward thekeyboard. "That's got to be the kill-code! The differencebetween their critical ma.s.ses! Seventy-four point eight!"

"Hold on," Susan said, peering over Soshi'sshoulder. "There's more here. Atomic weights. Neutroncounts. Extraction techniques." She skimmed the chart."Uranium splits into barium and krypton; plutonium doessomething else. Uranium has 92 protons and 146 neutrons,but-" "We need the most obvious difference," Midgechimed in. "The clue reads 'the primary differencebetween the elements.' "

"Jesus Christ!" Jabba swore. "How do we know whatTankado considered the primary difference?"

David interrupted. "Actually, the clue reads prime,not primary."

The word hit Susan right between the eyes. "Prime!" she exclaimed. "Prime!"

Shespun to Jabba. "The kill-code is a prime number! Thinkabout it! It makes perfect sense!"

Jabba instantly knew Susan was right. Ensei Tankado had builthis career on prime numbers. Primes were the fundamental buildingblocks of all encryption algorithms- unique values that had nofactors other than one and themselves. Primes worked well in codewriting because they were impossible for computers to guess usingtypical number-tree factoring.

Soshi jumped in. "Yes! It's perfect! Primes areessential to j.a.panese culture! Haiku uses primes. Threelines and syllable counts of five, seven, five. All primes.The temples of Kyoto all have-"

"Enough!" Jabba said. "Even if thekill-code is a prime, so what! There are endlesspossibilities!"

Susan knew Jabba was right. Because the number line wasinfinite, one could always look a little farther and find anotherprime number. Between zero and a million, there were over 70,000choices. It all depended on how large a prime Tankado decided touse. The bigger it was, the harder it was to guess.

"It'll be huge." Jabba groaned. "Whateverprime Tankado chose is sure to be a monster."

A call went up from the rear of the room. "Two-minutewarning!"

Jabba gazed up at the VR in defeat. The final shield wa.s.starting to crumble.

Technicians were rushing everywhere.

Something in Susan told her they were close. "We can dothis!" she declared, taking control. "Of all thedifferences between uranium and plutonium, I bet only one can berepresented as a prime number! That's our final clue.The number we're looking for is prime!"

Jabba eyed the uranium/plutonium chart on the monitor and threwup his arms. "There must be a hundred entries here!There's no way we can subtract them all and check forprimes."

"A lot of the entries are nonnumeric," Susanencouraged. "We can ignore them.

Uranium's natural,plutonium's man-made. Uranium uses a gun barrel detonator,plutonium uses implosion. They're not numbers, so they'reirrelevant!" "Do it," Fontaine ordered. On the VR, the final wallwas eggsh.e.l.l thin.

Jabba mopped his brow. "All right, here goes nothing. Startsubtracting. I'll take the top quarter. Susan, you've gotthe middle. Everybody else split up the rest. We're lookingfor a prime difference."

Within seconds, it was clear they'd never make it. Thenumbers were enormous, and in many cases the units didn'tmatch up.