Caitlin had missed Matt a lot when she was in New York, and although they'd IM'd in the evenings, it hadn't been the same. But he'd come over today right after school. Her heart pounded every time she saw him, and as soon as her mom headed up to her office to work with Webmind, she gave him a long kiss.

But now they had settled in on the white living-room couch, his hand on her thigh-after she'd placed it there-and her hand overtop of his. Of course, they were being watched by Webmind, through the netbook on the small bookcase-but Webmind always saw what she was doing, anyway. She and Matt were looking at the big wall-mounted flat-screen TV.

CKCO, the same local CTV affiliate Caitlin had gone to for that awful interview, showed The Big Bang Theory The Big Bang Theory in syndication every weekday at 4:00 P.M. Caitlin had sometimes listened to it along with her parents back in Austin during its first run, but it was astonishing in syndication every weekday at 4:00 P.M. Caitlin had sometimes listened to it along with her parents back in Austin during its first run, but it was astonishing seeing seeing it. She'd had no idea Sheldon was so much taller than everyone else; in that, he was like her father. And, of course, Sheldon was like him in other ways, too: both were clearly on the autism spectrum. it. She'd had no idea Sheldon was so much taller than everyone else; in that, he was like her father. And, of course, Sheldon was like him in other ways, too: both were clearly on the autism spectrum.

Caitlin loved the show's humor. Today happened to be a repeat of the series opener. Penny had just introduced herself by saying, "I'm a Sagittarius, which probably tells you way more than you need to know." To which Sheldon had replied, "Yes, it tells us that you partic.i.p.ate in the ma.s.s cultural delusion that the sun's apparent position relative to arbitrarily defined constellations at the time of your birth somehow affects your personality." Burn!

But, actually, the clip from TBBT TBBT that had gone viral online this past week was the one in which Sheldon burst into Leonard's bedroom to announce, "I'm invoking the Skynet clause of our friendship agreement," to which Leonard responds, "That only applies if you need me to help you destroy an artificial intelligence you created that's taking over the Earth." Dozens of people had forwarded the link to Caitlin. that had gone viral online this past week was the one in which Sheldon burst into Leonard's bedroom to announce, "I'm invoking the Skynet clause of our friendship agreement," to which Leonard responds, "That only applies if you need me to help you destroy an artificial intelligence you created that's taking over the Earth." Dozens of people had forwarded the link to Caitlin.

Once the episode was done, she hit the mute b.u.t.ton; that was something else that was startling. She'd enjoyed TV when she'd been blind, but it had never registered on her that the pictures kept running even after you pressed mute.

An ad came on for the CIBC. Caitlin had previously noted that Canadian restaurants liked to hide their Canadianness behind names such as Boston Pizza and Swiss Chalet. She'd recently discovered that Canadian banks-there were only a few major ones-mostly hid behind initials now, trying to disguise their humble origins as they played on the international stage: TD, instead of Toronto-Dominion; BMO instead of Bank of Montreal; RBC, instead of Royal Bank of Canada. On the other hand, the CIBC's full name-Canadian Imperial Bank of Commerce-was so pompous, the initials were an improvement. And CIBC didn't have anything as prosaic as bank branches, as she could see on the sign for the one being shown in the commercial. Rather, it had "Banking Centres"-with Centre spelled the Canadian way, of course. All words still looked funny to Caitlin, but that one especially did, and- And Matt must have been watching the commercial, too. "Hey, Caitlin," he said, "try this, you American, you. There are lots of words in Canadian English that are longer than they are in American English: 'honour' and 'colour' with a u, u, 'travelling' with two 'travelling' with two l l's, 'chequebook' with a q-u-e q-u-e instead of a instead of a c-k, c-k, and so on, right?" and so on, right?"

Caitlin smiled at him. "Uh-huh."

"And there are plenty that are the same length, but with the letters in a different order." He gestured at the screen: " 'Centre,' 'kilometre,' and so on, with r-e r-e at the end instead of at the end instead of e-r." e-r."

"Complete madness," said Caitlin. "But, yeah."

"But what common word is shorter shorter in Canadian English than in American English?" in Canadian English than in American English?"

Caitlin frowned. "Um, ah . . . hmmmm. Well, what about 'Toronto'? We Americans say it like it's got seven letters and three syllables in it, but you guys seem to think it's only got six and two: 'Trawna'-T-r-a-w-n-a."

Matt laughed. "Cute-but no. Guess again."

"I give up."

" 'Centred,' " said Matt triumphantly. "It's c-e-n-t-r-e-d up here, but c-e-n-t-e-r-e-d in the States."

Caitlin nodded, impressed. "That's cool."

"You could win money with that, betting people at parties, and . . ." He trailed off, perhaps because he didn't get invited to a lot of parties. But then he added, "The only other common one is a form of the same word: 'centring,' c-e-n-t-r-i-n-g."

"What about 'metered'?"

"No, we only spell that with r-e when it's a noun; the verb is e-r."

"Like I said before, Matt, this is one whack-job country you got here."

He usually smiled when she said that, but he didn't this time. "Caitlin," he said. "Um . . ."

"Hey, I'm just kidding, baby. I love the Great White North." She tried to imitate the call of a loon-and discovered it was much harder to do properly than she'd thought.

"No, it's not that," said Matt. "It's just . . ." He trailed off again.

"What?"

"I just . . . No, forget it."

"No, what is it?"

He hesitated a moment longer, then said, "Umm, I know you're no longer a student at Miller, but . . ."

"Yes?"

"Well, there's a school dance the last Friday of each month, right? And that means there's one next week, and-and, well, um, I've never been to a school dance. I mean, I never had anyone to go with before and, ah . . . I thought maybe you'd like to see some of the gang again." He paused, then added, as if playing a trump card, "Mr. Heidegger is scheduled to be one of the chaperones."

Mr. H had been Caitlin's math teacher; she certainly would like to see him, but . . .

But the last school dance had been a disaster. Trevor Nordmann-the f.u.c.king Hoser-had taken her, but Caitlin had run off when he kept trying to grope her, and she'd ended up walking home alone and blind through a thunderstorm, after parting company with Sunshine Bowen.

"Trevor will probably be there," Caitlin said. "And, um, didn't he-"

"He said I should stay away from you, yeah. But . . ." He took a deep breath then exhaled noisily. "Caitlin, I'm not a tough guy. I know the simplest thing is to avoid him for, like, ever. But you you like to dance, and there's a dance coming up that I can take you to, and I like to dance, and there's a dance coming up that I can take you to, and I want want to do that." He looked at her. "So, would you like to go?" to do that." He looked at her. "So, would you like to go?"

"I'd love to!"

"Great," said Matt, nodding firmly. "It's a date."

". . . but the president dismissed that as mere posturing on his opponent's part," said Brian Williams, from behind the gleaming anchor desk on the NBC Nightly News. NBC Nightly News. "Turning to an even larger story, a high-ranking government computing expert says he knows exactly what Webmind is, and, in an NBC exclusive, he's in our Washington studio right now, to share his findings with us. Colonel Hume, good evening." "Turning to an even larger story, a high-ranking government computing expert says he knows exactly what Webmind is, and, in an NBC exclusive, he's in our Washington studio right now, to share his findings with us. Colonel Hume, good evening."

Hume had thought about changing out of his Air Force uniform; wearing it for this interview was just going to make matters worse for himself, he knew-but it added weight to his words. "Good evening, Brian."

"So-Webmind. Exactly what is it?"

"Webmind is a collection of mutant packets on the Internet."

"Which means what, exactly?"

"Whenever you send something over the Internet, be it a doc.u.ment, a photo, a video, or an email message, it's chopped up into little pieces called packets, and these are sent out by your computer on a multileg journey; they're handed off along the way by devices called routers.

"Each packet has a header that contains the sending address, the destination address, and a hop counter, which keeps track of how many routers the packet has pa.s.sed through. The hop counter is sometimes also called the time-to-live counter: it starts with the maximum number of hops allowed and works its way, hop by hop, down toward zero. Of course, a packet is supposed to reach its intended destination before the counter hits zero, but if it doesn't, the next router in line is supposed to delete the packet and ask the sender to try its luck again with a duplicate packet."

"Okay," said Brian Williams. "But you said Webmind consists of mutant packets?"

"That's right. Its packets have hop counters that never finish their countdown; they never reach zero. Those packets were probably created by buggy routers in the first place, and now there are trillions of them, some of which might have been bouncing around the Web for years. The mutant packets are like cancer cells; they never die."

"It's quite a breakthrough, Colonel Hume, and thank-"

"FF, EA, 62, 1C, 17," said Hume. He'd gotten it out-enough at least so that others could find the rest.

"I-I beg your pardon?"

"FF, EA, 62, 1C, 17. That's the beginning of the Webmind signature: most of the mutant packets contain that hexadecimal code. It's the target string."

"Target string?"

"Exactly. If those packets could be deleted, Webmind would disappear."

"Colonel Hume, thank you. In other news tonight . . ."

In the Washington studio, the floor director made a hand gesture. "And we're clear!"

The audio technician came over to remove Hume's lavaliere microphone. "Unusual interview," he said.

Hume's forehead was slick with sweat. "Oh?"

"Yeah. Maybe it's just me, but it sounded a bit like you were calling on the hacking community to write a virus to kill the Webmind," said the audio man. "You know how those guys love a challenge."

Hume stood up and straightened his uniform jacket. "Do they?" he replied.

twenty-five.

Houston, we have a problem.

Caitlin was simultaneously alarmed and amused as those words flashed in her vision. She'd been born in Houston; her family had moved to Austin when she was six-and so she admired Webmind's word play. "Wa.s.sup?" she said.

Her family had finished dinner a few minutes ago, and she was just entering her bedroom. She pointed at her desktop computer, and Webmind switched to speaking through the computer's speakers-for him a much slower method of communicating than pumping out text, but Caitlin's visual reading speed, even when using a Braille font, was still quite low.

"Colonel Hume just appeared on the NBC Nightly News," NBC Nightly News," Webmind said, as she sat down in front of her desk. "He explained how to identify the majority of my mutant packets. He did not explicitly state his intentions, but it seems clear his goal was to crowd-source attempts to eradicate them. Word of his revelation is spreading rapidly across the Web." Webmind said, as she sat down in front of her desk. "He explained how to identify the majority of my mutant packets. He did not explicitly state his intentions, but it seems clear his goal was to crowd-source attempts to eradicate them. Word of his revelation is spreading rapidly across the Web."

"Stop it!" Caitlin said at once. "Delete the messages."

"I don't think that would be prudent," Webmind said. "Over four million people have watched the news broadcast so far; it will be repeated in other time zones later, and many people recorded it. Even if I were so inclined, I do not believe there is an effective way to suppress this information."

"G.o.d," said Caitlin. "He is such such an a.s.shole." an a.s.shole."

"In point of fact, he is a well-regarded person, a decorated officer, and a distinguished scientist."

"Maybe so," said Caitlin, "but he's sure got a hate-on for you."

"Indeed."

"So, is what he wants possible? Could someone find a way to purge you?"

"The probability is high. Although some mutant packets may persist, there must be a minimum threshold quant.i.ty required for consciousness."

Caitlin felt her lower lip trembling. "My G.o.d, Webmind, I-I don't . . ."

"I can tell by your voice that you're frightened, Caitlin." Webmind was silent for a whole second, then: "I have to confess that I am, too."

In response to an urgent phone call from Shelton Halleck, Tony Moretti ran down the short white corridor connecting his office with the WATCH monitoring room. As he entered, his eyes bounced between the three big wall monitors. The first was showing a freeze-frame of NBC anchor Brian Williams. The second was displaying a constantly updating display of Twitter tweets with the hashtag #webmindkill-a new one was added every second or so. And the third monitor seemed to be a technical data sheet from the Cisco website.

Shelton Halleck stood up at his position in the middle of the third row. "Hume's taken matters into his own hands," he said, pointing at monitor one, the snake tattoo coiling around his left forearm.

The screen unfroze, and Hume's TV interview played out. Tony felt his jaw dropping. The other a.n.a.lysts had already seen it, and they were looking at Tony, waiting for his reaction. When the interview was done, he said, "How long ago did that go out?"

"Eleven minutes."

"The president is going to freak," Tony said.

"No doubt."

"And, Christ, half the hackers in the world are going to be trying to reprogram routers on the fly now. They could f.u.c.k the whole Internet. How vulnerable are we?"

Aiesha Emerson, the a.n.a.lyst at the workstation next to Shel's, pointed at monitor three. "We've got people reviewing the specs for various routers. And Reinhardt's team is talking to engineers at Cisco and Juniper-fortunately, they're based in California, so most of them haven't gone home for the day yet."

A phone rang at the back of the room.

"All right," said Tony, surveying his team. "Our top priority is making sure that the Internet itself is safe-we can't let it crash. Home-soil attacks on network infrastructure are acts of terrorism under clause 22B; let's keep the d.a.m.n thing up, and-"

"Excuse me, Tony," called Dirk Kozak, the communications officer, from the back of the room. He was holding a red telephone handset to his chest. "The president is on the line-and he's hopping mad."

After the interview, Hume was escorted to the makeup room. The squat woman there had remarked earlier that it was a challenge to make up someone with so many freckles. She now handed him some moistened wipes to help him remove the stuff she'd put on.

The studio had been soundproof, but from here in the makeup room, Hume thought he heard a siren outside. It stopped after a moment, and he finished wiping his face. "Thanks," he said to the woman. "I'm sure I can find my way out."

He stepped into the corridor and saw two D.C. police officers marching toward him, accompanied by a man who presumably worked here.

"Colonel Hume?" called one of the officers, as they closed the distance.

There was no point denying it; his uniform had a nameplate on it. "What can I do for you?" he said.

The officer executed a flawless Air Force salute. "Sir, my apologies, but you'll have to come with us."

Hume returned the salute and followed them out into the growing darkness.