He steps off a curb, glancing reflexively to the left. A jingling sounds in his right ear, bicycle brakes trumpet. It is merely a Royal Marine (Waterhouse is beginning to recognize the uniforms) off on some errand; but he has reinforcements behind him in the form of a bus/coach painted olive drab and stenciled all over with inscrutable code numbers.

"Pardon me, sir!" the Royal Marine says brightly, and swerves around him, apparently reckoning that the coach can handle any mopping-up work. Waterhouse leaps forward, directly into the path of a black taxi coming the other way.

After making it across that particular street, though, he arrives at his Westminster destination without further life-threatening incidents, unless you count being a few minutes' airplane ride from a tightly organized horde of murderous Germans with the best weapons in the world. He has found himself in a part of town that seems almost like certain lightless, hemmed-in parts of Manhattan: narrow streets lined with buildings on the order of ten stories high. Occasional glimpses of ancient and mighty gothic piles at street-ends clue him in to the fact that he is nigh unto Greatness. As in Manhattan, the people walk fast, each with some clear purpose in mind.

The amended heels of the pedestrians' wartime shoes pop metallically. Each pedestrian has a fairly consistent stride length and clicks with nearly metronomic precision. A microphone in the sidewalk would provide an eavesdropper with a cacophony of clicks, seemingly random like the noise from a Geiger counter. But the right kind of person could abstract signal from noise and count the pedestrians, provide a male/female break down and a leg-length histogram-

He has to stop this. He would like to concentrate on the matter at hand, but that is still a mystery.

A massive, blocky modern sculpture sits over the door of the St. James's Park tube station, doing twenty-four hour surveillance on the Broadway Buildings, which is actually just a single building. Like every other intelligence headquarters Waterhouse had seen, it is a great disappointment.

It is, after all, just a building-orange stone, ten or so stories, an unreasonably high mansard roof accounting for the top three, some smidgens of classical ornament above the windows, which like all windows in London are divided into eight tight triangles by strips of masking tape. Waterhouse finds that this look blends better with classical architecture than, say, gothic.

He has some grounding in physics and finds it implausible that, when a few hundred pounds of trinitrotoluene are set off in the neighborhood and the resulting shock wave propagates through a large pane of glass the people on the other side of it will derive any benefit from an asterisk of paper tape. It is a superstitious gesture, like hexes on Pennsylvania Dutch farmhouses. The sight of it probably helps keep people's minds focused on the war.

Which doesn't seem to be working for Waterhouse. He makes his way carefully across the street, thinking very hard about the direction of the traffic, on the assumption that someone inside will be watching him. He goes inside, holding the door for a fearsomely brisk young woman in a quasimilitary outfit-who makes it clear that Waterhouse had better not expect to Get Anywhere just because he's holding the door for her-and then for a tired-looking septuagenarian gent with a white mustache.

The lobby is well guarded and there is some business with Waterhouse's credentials and his orders. Then he makes the obligatory mistake of going to the wrong floor because they are numbered differently here. This would be a lot funnier if this were not a military intelligence headquarters in the thick of the greatest war in the history of the world.

When he does get to the right floor, though, it is a bit posher than the wrong one was. Of course, the underlying structure of everything in England is posh. There is no in-between with these people. You have to walk a mile to find a telephone booth, but when you find it, it is built as if the senseless dynamiting of pay phones had been a serious problem at some time in the past. And a British mailbox can presumably stop a German tank. None of them have cars, but when they do, they are three-ton hand-built beasts. The concept of stamping out a whole lot of cars is unthinkable-there are certain procedures that have to be followed, Mt. Ford, such as the hand-brazing of radiators, the traditional whittling of the tyres from solid blocks of cahoutchouc.

Meetings are all the same. Waterhouse is always the Guest; he has never actually hosted a meeting. The Guest arrives at an unfamiliar building, sits in a waiting area declining offers of caffeinated beverages from a personable but chaste female, and is, in time, ushered to the Room, where the Main Guy and the Other Guys are awaiting him. There is a system of introductions which the Guest need not concern himself with because he is operating in a passive mode and need only respond to stimuli, shaking all hands that are offered, declining all further offers of caffeinated and (now) alcoholic beverages, sitting down when and where invited. In this case, the Main Guy and all but one of the Other Guys happen to be British, the selection of beverages is slightly different, the room, being British, is thrown together from blocks of stone like a Pharaoh's inner tomb, and the windows have the usual unconvincing strips of tape on them. The Predictable Humor Phase is much shorter than in America, the Chitchat Phase longer.

Waterhouse has forgotten all of their names. He always immediately forgets the names. Even ifhe remembered them, he would not know their significance, as he does not actually have the organization chart of the Foreign Ministry (which runs Intelligence) and the Military laid out in front of him. They keep saying "woe to hice!" but just as he actually begins to feel sorry for this Hice fellow, whoever he is, he figures out that this is how they pronounce "Waterhouse." Other than that, the one remark that actually penetrates his brain is when one of the Other Guys says something about the Prime Minister that implies considerable familiarity. And he's not even the Main Guy. The Main Guy is much older and more distinguished. So it seems to Waterhouse (though he has completely stopped listening to what all of these people are saying to him) that a good half of the people in the room have recently had conversations with Winston Churchill.

Then, suddenly, certain words come into the conversation. Water house was not paying attention, but he is pretty sure that within the last ten seconds, the word Ultra was uttered. He blinks and sits up straighter.

The Main Guy looks bemused. The Other Guys look startled.

"Was something said, a few minutes ago, about the availability of coffee?" Waterhouse says.

"Miss Stanhope, coffee for Captain Woe To Hice," says the Main Guy into an electrical intercom. It is one of only half a dozen office intercoms in the British Empire. However, it is cast in a solid ingot from a hundred pounds of iron and fed by 420-volt cables as thick as Waterhouse's index finger. "And if you would be so good as to bring tea."

So, now Waterhouse knows the name of the Main Guy's secretary. That's a start. From that, with a bit of research he might be able to recover the memory of the Main Guy's name.

This seems to have thrown them back into the Chitchat Phase, and though American important guys would be fuming and frustrated, the Brits seem enormously relieved. Even more beverages are ordered from Miss Stanhope.

"Have you seen Dr. Shehrrrn recently?" the Main Guy inquires of Waterhouse. He has a touch of concern in his voice.

"Who?" Then Waterhouse realizes that the person in question is Commander Schoen, and that here in London the name is apt to be pronounced correctly, Shehrrninstead of Shane.

"Commander Waterhouse?" the Main Guy says, several minutes later. On the fly, Waterhouse has been trying to invent a new cryptosystem based upon alternative systems of pronouncing words and hasn't said anything in quite a while.

"Oh, yeah! Well, I stopped in briefly and paid my respects to Schoen before getting on the ship. Of course, when he's, uh, feeling under the weather, everyone's under strict orders not to talk cryptology with him."

"Of course."

"The problem is that when your whole relationship with the fellow is built around cryptology, you can't even really poke your head in the door without violating that order."

"Yes, it is most awkward."

"I guess he's doing okay." Waterhouse does not say this very convincingly and there is an appropriate silence around the table.

"When he was in better spirits, he wrote glowingly of your work on the Cryptonomicon,"says one of the Other Guys, who has not spoken very much until now. Waterhouse pegs him as some kind of unspecified mover and shaker in the world of machine cryptology.

"He's a heck of a fella," Waterhouse says.

The Main Guy uses this as an opening. "Because of your work with Dr. Schoen's Indigo machine, you are, by definition, on the Magic list. Now that this country and yours have agreed-at least in principle-to cooperate in the field of cryptanalysis, this automatically puts you on the Ultra list."

"I understand, sir," Waterhouse says.

"Ultra and Magic are more symmetrical than not. In each case, a belligerent Power has developed a machine cypher which it considers to be perfectly unbreakable. In each case, an allied Power has in fact broken that cypher. In America, Dr. Schoen and his team broke Indigo and devised the Magic machine. Here, it was Dr. Knox's team that broke Enigma and devised the Bombe. The leading light here seems to have been Dr. Turing. The leading light with you chaps was Dr. Schoen, who is, as you said, under the weather. But he holds you up as comparable to Turing, Commander Waterhouse."

"That's pretty darn generous," Waterhouse says.

"But you studied with Turing at Princeton, did you not?"

"We were there at the same time, if that's what you mean. We rode bikes. His work was a lot more advanced."

"But Turing was pursuing graduate studies. You were merely an undergraduate."

"Sure. But even allowing for that, he's way smarter than me."

"You are too modest, Captain Waterhouse. How many undergraduates have published papers in international journals?"

"We just rode bikes," Waterhouse insists. "Einstein wouldn't give me the time of day."

"Dr. Turing has shown himself to be rather handy with information theory," says a prematurely haggard guy with long limp grey hair, whom Waterhouse now pegs as some sort of Oxbridge don. "You must have discussed this with him.

The don turns to the others and says, donnishly, "Information Theory would inform a mechanical calculator in much the same way as, say, fluid dynamics would inform the hull of a ship." Then he turns back to Waterhouse and says, somewhat less formally: "Dr. Turing has continued to develop his work on the subject since he vanished, from your point of view, into the realm of the Classified. Of particular interest has been the subject of just how much information can be extracted from seemingly random data."

Suddenly all of the other people in the room are exchanging those amused looks again. "I gather from your reaction," says the Main Guy, "that this has been of continuing interest to you as well."

Waterhouse wonders what his reaction was. Did he grow fangs? Drool into his coffee?

"That's good," says the Main Guy before Waterhouse can answer, "because it is of the highest interest to us as well. You see, now that we are making efforts-and I must emphasize the preliminary and unsatisfactory level of these efforts to this point-to coordinate intelligence between America and Britain, we find ourselves in the oddest situation that has ever faced a pair of allies in a war. We know everything, Commander Waterhouse. We receive Hitler's personal communications to his theater commanders, frequently before the commanders do! This knowledge is obviously a powerful tool. But just as obviously, it cannot help us win the war unless we allow it to change our actions. That is, if, through Ultra, we become aware of a convoy sailing from Taranto to supply Rommel in North Africa, the knowledge does us no good unless we go out and sink that convoy."

"Clearly," Waterhouse says.

"Now, if ten convoys are sent out and all of them are sunk, even those under cover of clouds and darkness, the Germans will ask themselves how we knew where those convoys could be found. They will realize that we have penetrated the Enigma cypher, and change it, and then this tool will be lost to us. It is safe to say that Mr. Churchill will be displeased by such an outcome." The Main Guy looks at all of the others, who nod knowingly. Waterhouse gets the feeling that Mr. Churchill has been bearing down rather hard on this particular point.

"Let us recast this in information theory terms," says the don. "Information flows from Germany to us, through the Ultra system at Bletchley Park. That information comes to us as seemingly random Morse code transmissions on the wireless. But because we have very bright people who can discover order in what is seemingly random, we can extract information that is crucial to our endeavors. Now, the Germans have not broken our important cyphers. But they can observe our actions-the routing of our convoys in the North Atlantic, the deployment of our air forces. If the convoys always avoid the U-boats, if the air forces always go straight to the German convoys, then it is clear to the Germans-I'm speaking of a very bright sort of German here, a German of the professor type-that there is not randomness here. This German can find correlations. He can see that we know more than we should. In other words, there is a certain point at which information begins to flow from us back to the Germans."

"We need to know where that point is," says the Main Guy. "Exactly where it is. We need then to stay on the right side of it. To develop the appearance of randomness."

"Yes," Waterhouse says, "and it has to be a kind of randomness that would convince someone like Rudolf von Hacklheber."

"Exactly the fellow we had in mind," the don says. "Dr. von Hacklheber, as of last year."

"Oh!" Waterhouse says. "Rudy got his Ph.D.?" Since Rudy got called back into the embrace of the Thousand-Year Reich, Waterhouse has assumed the worst: imagining him out there in a greatcoat, sleeping in drifts and besieging Leningrad or something. But apparently the Nazis, with their sharp eye for talent (as long as it isn't Jewish talent) have given him a desk job.

Still, it's touch and go for a while after Waterhouse shows pleasure that Rudy's okay. One of the Other Guys, trying to break the ice, jokes that if someone had had the foresight to lock Rudy up in New Jersey for the duration, there would be no need for the new category of secret known as Ultra Mega. No one seems to think it's funny, so Waterhouse assumes it's true.

They show him the organizational chart for RAE Special Detachment No. 2701, which contains the names of all of the twenty-four people in the world who are on to Ultra Mega. The top is cluttered with names such as Winston Churchill and Franklin Delano Roosevelt. Then come some other names that seem oddly familiar to Waterhouse-perhaps the names of these very gents here in this room. Below them, one Chattan, a youngish RAF colonel who (Waterhouse is assured) accomplished some very fine things during the Battle of Britain.

In the next rank of the chart is the name Lawrence Pritchard Waterhouse. There are two other names: one is an RAF captain and the other is a captain in the United States Marine Corps. There is also a dotted line veering off to one side, leading to the name Dr. Alan Mathison Turing. Taken as a whole, this chart may be the most irregular and bizarre ad-hocracy ever grafted onto a military organization.

In the bottom row of the chart are two groups of half a dozen names, clustered beneath the names of the RAF captain and the Marine captain respectively. These are the squads that represent the executive wing of the organization: as one of the guys at the Broadway Building puts it, "the men at the coal-face," and as the one American Guy translates it for him, "this is where the rubber meets the road."

"Do you have any questions?" the Main Guy asks.

"Did Alan choose the number?"

"You mean Dr. Turing?"

"Yes. Did he choose the number 2701?"

This level of detail is clearly several ranks beneath the station of the men in the Broadway Buildings. They look startled and almost offended, as if Waterhouse has suddenly asked them to take dictation.

"Possibly," says the Main Guy. "Why do you ask?"

"Because," Waterhouse says, "the number 2701 is the product of two primes, and those numbers, 37 and 73, when expressed in decimal notation, are, as you can plainly see, the reverse of each other."

All heads swivel toward the don, who looks put out. "We'd best change that," he says, "it is the sort of thing that Dr. von Hacklheber would notice." He stands up, withdraws a Mont Blanc fountain pen from his pocket, and amends the organizational chart so that it reads 2702 instead of 2701. As he is doing this, Waterhouse looks at the other men in the room and thinks that they look satisfied. Clearly, this is just the sort of parlor trick they have hired Waterhouse to perform.