The Alfa roared down the street.

`He wasn't expecting the roadblock,' Graves said. `He didn't count on that.'

`Whose side are you on?' Phelps demanded.

At the end of the street four policemen waited by the parked patrol car. As the Alfa bore down on them,they dropped to their knees, holding their guns stiffarmed before them.

`Don't shoot!' Graves screamed.

The cops began to fire. The tyres on the Alfa exploded. The front windshield shattered. The car wobbled, flipped on its side, and slammed into a parked car. The horn began to blare.

Graves ran over to the Alfa and tried to open the door. It was jammed shut. He looked in through the shattered windscreen and saw Wright's face, a bloody pulp, the features indistinguishable. As he watched, a tiny stream of blood spurted rhythmically from Wright's neck. Then it became a seeping red stain across his collar.

He turned away from the car.

`Is he dead?' Phelps said, running up.

`Yes,' Graves said. `He's dead.'

`How can we turn off that fucking horn?' Phelps said.

Graves stared at him and walked away.

HOUR 1
SAN DIEGO
4 PM PDT

His sense of shock was profound. Of all the alternatives, of all the possibilities and options, he had never expected this. He had never expected Wright to die.

Graves walked back up the street slowly, trying to gather his thoughts. What did he do next?

Nordmann came up to him. `That's a damned shame,' he said.

`You bet it is,' Graves said.

Nordmann looked at the crowd clustered around the wrecked car. `One thing, though,' he said.

`What's that?'

`It proves he could make a mistake.'

`It was a big one,' Graves said.

`Yes,' Nordmann said, in a calm, logical voice. `But it was a mistake.'

Graves nodded and walked back towards the surveillance building. He thought about what Nordmann had said. The more he thought about it, the more encouraged he was. Because Nordmann was right.

Wright had erred. And that was encouraging.

One of the aides came running out of the building, waving Wright's ticket. `Mr Graves,' he said. `There's something very strange going on. We just checked this ticket. He cancelled that reservation yesterday.'

Protect me from fools, Graves thought. `Of course he did.'

`Of course?'

`Look,' Graves said. `He planned to let us catch him, and he planned his escape. But he couldn't get far if we knew his real aeroplane reservation, could he?'

`Well, I guess not...'

`Keep checking the airlines. Check Los Angeles, too. You'll find he had a reservation somewhere.'

Phelps came over. `The sniffer's arrived.'

`Has it? Good.' Graves walked across the street to Wright's apartment building. Phelps trailed behind him in silence.

Finally Phelps said, `I hope you know what you're doing.'

Graves didn't answer. Because the fact was that he didn't know what he was doing. He knew only in a general way what Wright intended. Wright had made Graves a part of the total mechanism, and therefore Graves would have to cancel himself out - inactivate himself - by not doing what was expected of him.

In order to do that, he had to decipher as many elements of the total staging mechanism as possible. Only then could he determine how he was intended to participate in the staging sequence that controlled the final release of the gas.

The sniffer was the first step in deciphering the sequence.

Graves stood outside the door to Wright's apartment. Next to him Lewis held a gunlike instrument in his hand. The gun was attached to a shoulder pack with a dial. Lewis pointed the instrument at the door and ran it along the cracks and seams.

Behind them at the far end of the hallway, six people, including Phelps, stood and watched. Graves wanted everyone away from the door so that they wouldn't accidentally trip the vibration sensors. He didn't know how sensitively they were tuned, but he wasn't taking any chances.

After a moment Lewis turned away with the instrument. `Wow,' he said.

`You get a reading?'

`Yeah,' he said. `High nitrogen and oxygen content, trace phosphorus.'

`Meaning?'

`Plastic explosive, very near.'

`Near the door?'

`Probably just on the other side,' he said.

Graves said, `Is there any chance you're wrong?'

`The sniffer is never wrong,' he said. `You've got oxide of nitrogen fumes, and that's explosives. You can count on it.'

`All right,' Graves said. He walked away from the door. He had to trust the sniffer. It had been developed for use in Vietnam and had been adapted for customs operations, smuggling, and so on. It was incredibly sensitive and incredibly accurate. If the sniffer said plastic explosive was behind the door, he had to believe it. He walked back to Phelps at the end of the hallway.

`Well?'

`There's explosive on the other side of the door.'

`Nice,' Phelps said. `What do we do now?'

`Try to get a better look inside the apartment,' Graves said. He glanced at his watch.

`It's four ten,' Phelps said. `When did your friend say it would go off?'

`Five,' Graves said.

`I hope you know what you're doing,' Phelps said again.

Graves sighed. He wondered if he could ever explain to Phelps that that wasn't the problem. The problem was figuring out what Wright expected him to do - and then not doing it.

Across the street in the surveillance room looking down on Wright's apartment, he talked to Nordmann. Nordmann had brought a cardboard box full of medical supplies - syringes, needles, bottles of liquid. He was frowning down at it. `This is the best I could manage on short notice,' he said.

`Will it work?' Graves said.

`It's the standard therapy,' Nordmann said. `But we haven't got much. This quantity will treat two or three people for exposure, that's all.'

`Then let's make sure it doesn't come to that.'

Nordmann smiled slightly. `It better not,' he said. `Because you need somebody alive and well to administer it.'

`Is it hard to administer?'

`Tricky,' Nordmann said. `There are two different chemicals, atropine and parladoxime. They have to be balanced.'

Graves sighed. `So the antidote is a binary, too.'

`In a sense. The two chemicals treat different effects of the gas. One treats the peripheral nervous system, the other the central. The chemicals are dangerous in themselves, which makes it all much harder.'

`Fighting fire with fire?'

`In a sense,' Nordmann said.

The two men stood staring out the window at the apartment opposite. Phelps was in a corner using a walkie-talkie. `You in position?'

A response crackled back. `In position, sir.'

`Very good.' Phelps clicked off the walkie-talkie. `We've got two cops stationed outside the door to that apartment,' he said.

`Fine,' Graves said. `Just so they don't get too close to the door.'

`I have them ten feet away.'

`That should be fine.'

In the hallway outside Wright's apartment, officers Martin and Jencks of the San Diego Police Department stared at the closed door and leaned against the wall.

`You understand any of this?' Jencks said.

`Nope,' Martin said.

`But they said not to get too close to the door.'

'That's right.'

`You know why?'

`I don't know nothing,' Martin said. He took out a cigarette. `You got a match?'

`Maybe we shouldn't smoke...'

`Who's going to know?' Martin said.

Jencks gave him a match.

Graves stood with Nordmann in the surveillance room across the street.

'Wright booby-trapped the apartment?'

`Elaborately,' Graves said. `He told me some of it. I'm sure he didn't tell me everything.'

`And it goes off at five?'

`Yes.'

`Forty-five minutes from now,' Nordmann said. `Is the Navy sending people with protective suits? Because protected people could just walk right in.'

`Nobody can walk right in,' Graves said. `He's wired the room with explosive. That's why we've got the guards over there.'

Nordmann grimaced. `Explosive?'

`Twenty pounds of it.'

The TV in the corner of the room showed the Convention. A monotonous voice was saying, `Mr Chairman... Mr Chairman, we request the floor... Mr Chairman...' There was the loud banging of a gavel.

`Turn that damned thing off,' Graves said. Someone turned it off.

At the window two men grunted as they lifted a huge lens onto a heavy-duty tripod. It was screwed into place and adjusted. `Ready, Mr Graves.'

`Thank you.' Graves went to the window.

`What's that?' Nordmann said.

`A fifteen-hundred-millimeter telephoto,' Graves said. `It's the best look we can get.'

He peered through the giant lens. The view was so enormously magnified that at first he didn't know what he was looking at. Using a fine-knurled knob, he moved the lens and saw he was focused on a crack in the floor. He moved across the floor to the boxes. He shifted the lens upward, examining each box in detail.

`Take a look at this,' he said, stepping away.

Nordmann squinted through the lens. `Three stacked boxes,' he said. `I can't make out much...'

`Neither can L' Graves folded his arms across his chest and stared out the window. He tried to think logically, but he was having trouble; Wright's death had unnerved him, whether he wanted to admit it or not.

And the system seemed so complicated. Staging sequences, timers, vibration sensors, explosives... His head ached. How the hell would he unravel it?

`Let's work it backward,' Nordmann said. `What's the most important element in the system?'

`The gas.'

`How is it controlled?'

`There are spring-loaded valve mechanisms. They can be tripped by a solenoid.'

`And they presumably have a timer of some kind.'

`Presumably.'

`Battery-powered or line-powered?'

`Well, he's plugged one of the boxes into the wall. But the valve mechanisms are probably batterypowered.'

Nordmann nodded. `That makes sense,' he said. `He wouldn't have the most important elements dependent on an external system. So what did he plug into the wall?'

`I don't know.'

`Vibration sensors?'

`Maybe,' Graves said. He looked at his watch. It was 4:20. He would have to move soon. What had Wright expected him to do? The psychological report was folded up in his pocket. He took it out and looked at the last few lines.

IF THERE ARE ANY DEFECTS OR HIDDEN FLAWS IN HIS BEHAVIOUR, THEY ARE HIS IMPULSIVENESS AND HIS DESIRE TO FINISH A TEST SITUATION RAPIDLY.

Well, he didn't have much choice now. He was going to have to make a move, and soon.

`You know,' Nordmann said thoughtfully, `most of the equipment in that room is defensive. It's designed to keep people out of there until the gas is ready to be released. But I suspect some of those defences. are meant to be penetrated.'

`I agree,' Graves said. `And in any case, we have to start penetrating.'

`Wall current first?' Nordmann asked.

Graves nodded. He glanced at Phelps, who was sitting in a corner of the room literally chewing his nails. Graves sent Lewis across the street to disconnect power to the apartment. Four minutes later, the power was off. Graves watched through the big telephoto lens. He saw a single yellow pilot light in the vibration sensor box go out.

`Well,' Nordmann said, `that's a start. We've killed part of the system.'

`Have we?' Graves said. He watched through the telephoto as the solenoid mechanism tripped open the tank valves, then a moment later tripped them shut.

The apartment became filled with whitish gas.

`What's happening?' Phelps said, very agitated.

`Quick,' Graves said. `Those cops. Tell the cops.'

`What cops?' Phelps said.

Officer Martin finished his cigarette and ground it out on the floor. His heel squeaked.

`Sssh,' Jencks said, suddenly tense.

`What is it?'

`Sssssh. Listen.'

The two men listened in silence. There was a hissing. `You hear that?' Jencks said.

`Yeah. It's coming from the room.'

`Are you sure?'

Martin moved closer to the door. `I think so -'

`Maybe you shouldn't -'

Martin began to cough. His nose ran. `Shit,' he said. `What is this?' He coughed again.

Jencks went forward to help him. Then Jencks felt the stinging in his nostrils, and the liquid began to pour over his shirt. He didn't know a nose could run that way. His eyes ached and stung; he felt dizzy. `What the hell...' He had a coughing fit.

The walkie-talkie crackled. `This is Phelps,' a voice said. `Over.'

Martin took a step towards the walkie-talkie and fell to the floor. Now he could see the faint wispy whiteness seeping through the door.

`This is Phelps. Over.'

Jencks was coughing loudly and groaning.

Martin stretched out his hand towards the walkietalkie. He was weak. His arm trembled. Then, without warning, he vomited and lost consciousness.

`I'm not getting an answer,' Phelps said.

Graves and Nordmann exchanged glances, then looked back out the window at the opposite apartment. The room now had a faint milky haze.

`Are they dead?' Phelps said.

`Probably.'

`How can you just stand there?F

'Because,' Graves said, `it was just a short burst. The valves are turned off again.'

Phelps looked puzzled.

`It wasn't a full release,' Graves said. `It's just a partial release, to fill the room with gas. That's why Wright carefully closed the windows. Now we really can't get in there.'

`You sound so appreciative,' Phelps said.

`I'm not. But we understand now what Wright meant by a complex staging sequence.'

`God damn it, this is not a jigsaw puzzle! Two cops have died and -'

`We're all right,' Nordmann said quietly, `until five PM.,

'And what do you intend to do between now and then?' Phelps demanded angrily. `I'm going to call the Navy,' he said. `Their men were supposed to be here an hour ago. It's four thirty now.'

Graves stared at the gas-filled apartment. He had a brief mental image of the two cops staggering drunkenly in the hallway. He pushed it away; he could consider it later.

Beside him Nordmann said, `It's really quite clever.'

Graves said, `How thick is the gas in that room?'

`Hard to say,' Nordmann said. `The normal colour of the gas is white. I don't think the density is very great. Why?'

`If you shot me full of those antidotes, could I survive the atmosphere in that room?'

`I don't know.'

`Would I have a chance?'

`A chance? Of course. But even if you could survive, how would you get in? You said yourself it's wired with explosives. You can't go in the front door.'

`I wasn't thinking of the door,' Graves said. `I was thinking of the window.'