The girl looks at her in amazed revulsion, as though Cayce were a cat bringing up a particularly repellant hairball.

"All right," says Cayce, under her breath, to the girl's receding back, "be French."

But her coffee does arrive, and is excellent, as do her eggs and sausage, very good as well, and when she's finished she looks up to see Voytek staring at her. Prion is gone.

"Casey," he says, remembering but getting it wrong.

"That was Billy Prion, wasn't it?"

"I join you?"

"Please."

He repacks his spiral-bound notebooks, closing each one and tuck-ing it carefully away into his shoulder pouch, and crosses to her table. "Is Billy Prion a friend of yours?"

"Owns gallery. I need space to show ZX 81 project."

"Is it finished?"

"I am still collecting ZX 81."

"How many do you need?"

"Many. Patronage also."

"Is Billy in the patronage business as well?"

"No. You work for large corporation? They wish to learn of nay project?"

"I'm freelance."

"But you are here to work?"

"Yes. For an advertising agency."

He adjusts the pouch on his lap. "Saatchi?"

"No. Voytek, do you know anything about watermarking?"

He nods. "Yes?"

"Steganography?"

"Yes?"

"What might it mean if something, say a segment of digitized video, is watermarked with a number?"

"Is visible?"

"Not ordinarily, I don't think. Concealed?"

"That is the Steganography, the concealment. Multi-digit number?"

"Maybe."

Can be code supplied to client by watermarking firm. Firm sells client stego-encrypted watermark and means to conceal. Check web for that number. If client's image or video has been pirated, that is revealed by search."

"You mean you could use the watermark to follow the dissemination of a given image or video clip?"

He nods.

"Who does this, the actual watermarking?"

"There are companies."

"Could a watermark be traced to a particular company, its number?"

"Would not be so good for client security."

"Would it be possible for someone to detect, or extract, a secret watermark? Without knowing the code, or who placed it there, or even being sure it's there in the first place?"

Voytek considers. "Difficult, but might be done. Hobbs knows these things."

"Who's Hobbs?"

"You meet. Man with Curtas."

Cayce remembers the mean Beckett face, the filthy fingernails. "Really? Why?"

"Maths. Trinity, Cambridge, then works for United States. NSA. Very difficult."

"The work?"

"Hobbs."

THE Children's Crusade is remounting in force, this sunny morning.

She stands in Aberdeen with Voytek, watching them troop past, looking dusty in this sunlight and medieval, slouching not toward Bethlehem but Camden Lock.

Voytek has put on a pair of shades with small round lenses. They remind Cayce of coins placed on the eyes of a corpse.

"I must meet Magda," he announces.

"Who is she?"

"Sister. She is selling hats, in Camden Lock. Come." Voytek pushes off into the current of bodies, clockwise, "Saturday sells in Portobello, the fashion market. Sunday, here." Cayce follows, thinking, framing questions about watermarking.

The sun on this shuffling press is soothing, and they soon arrive at the lock, carried along by a current of feet responsible for all those billions in athletic-shoe sales.

Voytek has implied that Magda, aside from designing and making hats, does something in advertising herself, although Cayce can't quite make out what it is.

The market is set back in a maze of Victorian brick.

Warehouses, she supposes, and subterranean stables for the horses that drew the barges down the canals. She isn't certain she's ever really gotten to the bottom of the labyrinth, though she's been here many times. Voytek leads the way, past sheet-hung stalls of dead men's clothes, film posters, recordings on vinyl, Russian alarm clocks, sundries for smokers of anything but tobacco.

Deeper into the brickwork vaults, away from the sun, illuminated by Lava lamps and fluorescents in nonstandard colors, they find Magda, who aside from those cheekbones looks nothing at all like her brother. Short, pretty, hennaed, laced into a projectile bodice that seems to have been retrofitted from some sort of pressurized flying gear, she is happily packing her goods and preparing to close her stall.

Voytek asks her something in whatever their native tongue is. She answers, laughing.

"She says men from France buy wholesale," Voytek explains.

'"She speak good English,'" Magda says to Cayce. "I'm Magda." Cayce Pollard." They shake hands.

Casey is advertising too."

'Probably not the way I am, but don't remind me," says Magda, wrapping another hat in tissue and putting it into a cardboard carton with the rest.

Cayce starts to help. Magda's hats are hats that Cayce could wear, if she wore hats. Gray or black only, knit, crocheted, or yarn-stitched with a sailor's needle from thick industrial felt, they are without period or label. "These are nice."

"Thank you."

"You're in advertising? What do you do?"

"Look sorted, go to clubs and wine bars and chat people up. While I'm at it, I mention a client's product, of course favorably. I try to attract attention while I'm doing it, but attention of a favorable sort. I haven't been doing it long, and I don't think I like it."

Magda does indeed speak good English, and Cayce wonders at the difference in their fluencies. But says nothing.

Magda laughs. "I really am his sister," she says, "but our mother brought me here when I was five, thank God." Putting away the last hat, she closes the carton and hands it to Voytek.

"You're paid to go to clubs and mention products?"

"Firm's called Trans. Doing very well, apparently. I'm a design student, need something to make ends meet, but it's getting to be a bit much." She's lowering a sheet of tattered transparent plastic to indicate that her makeshift stall is now closed. "But I've just sold twenty hats! Time for a drink!"

"YOU'RE in a bar, having a drink," Magda says, the three of them wedged into one darkly varnished corner of an already raucous Camden pub, drinking lager.

"I know," says Voytek, defensively.

"No! I mean you're in a bar, having a drink, and someone beside you starts a conversation. Someone you might fancy the look of. All very pleasant, and then you're chatting along, and she, or he, we have men as well, mentions this great new streetwear label, or this brilliant little film they've just seen. Nothing like a pitch, you understand, just a brief favorable mention. And do you know what you do? This is what I can't bloody stand about it: Do you know what you do?"

"No," Cayce says.

"You say you like it too! You lie! At first I thought it was only men who'd do that, but women do it as well! They lie!"

Cayce has heard about this kind of advertising, in New York, but has never run across anyone who's actually been involved in it. "And then they take it away with them," she suggests, "this favorable mention, associated with an attractive member of the opposite sex. One who's shown some slight degree of interest in them, whom they've lied to in an attempt to favorably impress."

"But they buy jeans," Voytek demands, "see movie? No!"

"Exactly," Cayce says, "but that's why it works. They don't buy the product: They recycle the information. They use it to try to impress the next person they meet."

"Efficient way to disseminate information? I don't think."

"But it is," Cayce insists. "The model's viral. 'Deep niche.'The venues would be carefully selected—"

"Bloody brilliantly! That's the thing, I'm every night to these bleeding-edge places, cab fare, cash for drinks and food." She takes a long pull on her half pint. "But it's starting to do something to me. I'll be out on my own, with friends, say, not working, and I'll meet someone, and we'll be talking, and they'll mention something."