"That means a small bomb."

"Small enough to fit in your pocket — big enough to zap twenty or thirty people." Mellor quoted the figures without relish. "I don't like this, Carry. We've called in all patrols, but they're way out in the sticks and it's going to be twenty minutes before anybody shows."

"Tell them to come in low and quiet, and to land at least a kilometre away from the Street — if our visitor sees any fliers he's likely to pop his cork." Dallen was getting into his car as he spoke. "Can you tell which way he's heading?"

"He was sniffed out on the corner of Ninth, and then on Eighth. My guess is he'd heading for the Exhibition Centre itself. Going for the biggest number of casualties."

"Naturally." Cursing the scant Metagov funding which forced him to monitor the region with inadequate resources, Dallen switched on the car's pulse-magnet engine and drove down the hill towards 1990 Street. Rumours that a show-piece terrorist attack was imminent had been circulating for weeks, ever since he had intercepted a group coming up from Cordele and two of its members had thed in the subsequent chase. He had given little regard to the stories, and even less to the refined versions which predicted an attempt on his own life, mainly because there was no special action he could take. His field force of sixteen officers was permanently overstretched, and now it looked as though a price might have to be paid.

Speaking without moving his lips, purely for the benefit of the transceiver in his ear, Dallen said, "Are there many tourists in the museum sector?"

"Not too many," Mellor replied. "Four or five hundred, and maybe a quarter of those are in the Exhibition Centre. Do you want me to start pulling them out?"

"No! That could trigger the crazy bastard off quicker than anything. Can you get a new fix on his position?"

"Sorry. There's practically no signal left in that fuse. It must have been a freak condition that let us pick it up on Eighth and Ninth, and I don't know if it'll happen anywhere else."

"Okay, but keep me posted — Fm going to walk up 1990 Street from the Centre and see if I can spot him."

There was a brief silence. "That's not part of your job, Carry."

"I'll give myself a reprimand later." The car's engine whined in protest as Dallen angled it down the hill in a series of high-speed swerves, cleaving occasional puddles into silver spray, using the full width of each street and jolting over sidewalk corners where necessary. His knowledge that there was little risk of colliding with another vehicle and none at all of harming pedestrians gave him licence to drive in a manner which would have been unthinkably reckless in normal surroundings. From the air, the Scottish Hill district looked like an ordinary suburb, but all its houses and stores had been empty for decades, sealed by near-invisible plastic skins which proofed their structures against decay. Most of Madison City was similarly deserted, similarly preserved, with time switches bringing on the street and house lights at dusk for the benefit of families who had long since emigrated to the Big O.

Reaching the edge of the museum district, Dallen turned the car into a cross-street and slowed down. He was less than a block away from 1990 Street itself and was entering the "living" sector of the permanent display. Solid images of cars and other vehicles — all of late 20th Century design — moved purposefully ahead of him, and seemingly real people in the costume of the period thronged the sidewalks and went in and out of stores.

The images had been closely packed to create an impression of overcrowded city life on Earth three centuries earlier, before the discovery of Orbitsville. Stationary cars formed a continuous line on each side of the street, apparently leaving no room for Dallen to park, but he knew the illusion was the least of his problems. He drove directly into a resplendent white Cadillac, unable to prevent himself flinching in the instant when the front of his own car burrowed into the convincingly real bodywork of the larger vehicle and braked sharply. Sounds and smells of Madison circa 1990, accurately reproduced by hidden machines, enveloped him as he got out of the car and began walking north towards the next intersection.

"Carry! 1 think we just got another whisper near the corner of 1990 and Third." The voice in Dallen's ear now had a discernible edge of nervousness. "He's getting too near the Exhibition Centre."

"I'm on First, turning into 1990 two blocks east of him," Dallen responded. "Assuming we walk about the same speed, that means we should meet up near the corner of Second. It shouldn't be too hard to pick him out. "Him or her."

"The masculine pronoun covers both genders — specially in this line of business. Aware that he had put too much effort into trying to sound pedantic and cool, Dallen brought his dunking into tighter focus. Isn’t the TL37 a dual-action fuse?"

"Yeah — timer and impact," Mellor confirmed. "That means if you don't immobilise him real fast he's liable…"

"1 know what it means, Jim. Dallen negotiated the remaining distance to the intersection, stepping around the animated solid images as though they were real people, partly from instinct and also because there was a sprinkling of tourists in the simulated crowd. In most cases he could identify holiday-makers by the current fashions of their clothing, but some liked to dress in period for their venture into 1990 Street and it could be quite difficult to distinguish them from holomorphs.

He paused at the corner and took stock of his surroundings. A short distance to his right were the crystalline palisades of the Exhibition Centre; at successive intersections directly ahead were A. D. 2090 Street and A.D.2190 Street, each a recreation of its own historical era; and to his left were the seething perspectives of a Madison City thoroughfare as it had looked three centuries earlier. And somewhere in that oppressive confusion of human beings and holomorphs there lurked a terrorist who was getting ready to ply his trade.

Dallen's confidence wavered as it came to him that he did not even know if his quarry -was on the north or south side of the street. The images of the buses and commercial vehicles which jammed the central pavement were impenetrable to the eye, every bit as good as the real thing for providing an intruder with cover. Dallen slipped his right hand into the side pocket of his jacket and gripped the flat shape of his official sidearm. He rotated its beam control, setting the Weapon to emit a broad fen of energy. It was unlikely that he would get enough time for precise marksmanship, and rather than miss his target altogether it would be better to bring down half-a-dozen bystanders and let them denounce him while they recovered in hospital.

"I'm walking east on 1990," he sub vocalised. "If I reach the corner of Second without making contact I'm going to assume the bandit is either near me or has got past me. Til wait thirty seconds then I'll say "off. As soon as I do that I want you to throw the switch and kill every image projector in the Street. That should take our visitor by surprise and give me a couple of seconds to pick him out."

"Okay, Carry" Mellor said, "but suppose there's more than one."

"It won't matter — Tin geared up to paralyse half the Street."

Tm with you."

"Be glad you aren't." Dallen moved tentatively along the block, grateful that fashions in men's casual clothing had varied little over the centuries. His tan jacket, slacks and open-necked shirt made a virtually timeless ensemble which enabled him to mingle unobtrusively with tourists and holomorphs alike. He kept to the outer edge of the sidewalk, trying to scan both sides of the Street at once. His task was made a little easier by the fact that he could remember some of its permanent, though insubstantial, residents. There was the newspaper seller at the entrance to the Clarence Hotel, the amiably tubby guard at the bank, the cigar store owner who grinned his idealised grin at passers-by. Figures who paused and spoke to them, obeying their programmes, were immediately identifiable as holomorphs, as were taxi drivers, delivery men and the tike.