He failed to answer her question. His mouth hung open as if in astonishment, as though he couldn't quite believe that he had put the Expedition through a controlled spin or that he was barreling across the median toward the westbound lanes.

All right, he wasn't barreling yet, but the truck continued to accelerate as it reached the low point of the swale. If they crossed the declivity and hit the rising slope at the wrong angle and at too high a speed, the SUV would roll because rolling was something that SUVs did well when they were badly driven and when the terrain was, like this, composed of shifting sand and loose shale.

She shouted – 'Don't!' – but he did. As the Expedition churned across the crumbling face of the upgrade, Jilly jammed her feet harder against the dashboard, wondering where the impact air bag might be stowed, dreading what would happen if the bag was in the dashboard and if it exploded around her feet, wondering whether it would jam her knees into her face, whether it would rupture around her shoes and spew skin-peeling hot gas at high pressure across her entire body. Those grotesque images and worse flashed through her mind, instead of the standard replay of her life to date (with the Looney Tunes soundtrack that would have been most appropriate), but she couldn't block them, so she held fast to the seat and to the assist bar and shouted – 'Don't!' – again to no avail.

Riddling the night behind them with twin barrages of tire-cast shale and sand, Dylan forced the Expedition up the northern incline of the median at an oblique angle, putting the vehicle to the ultimate roll test. Judging by the relentlessness with which gravity pulled Jilly toward the driver, just one more degree of tilt would tumble the SUV back into the swale.

Repeatedly as they ascended, four-wheel drive seemed to be at least two wheels shy of an adequate number to maintain traction. The truck lurched, rocked, but finally topped the rise onto the shoulder of the westbound lanes.

Dylan checked the rearview mirror, glanced at the side mirror, and rocketed into a gap in traffic, heading back the way they had come. Toward town. Toward the motel where the Coupe DeVille no doubt still smoldered. Into the trouble they had been trying to outrun.

Jilly had the crazy notion that the dangerous crossing of the median had been motivated by Shep's reminder – 'Fries not flies' – that he had not eaten dinner. The older brother's impressively deep commitment to the younger was admirable to a point, but a return to that burger bistro under these circumstances represented a colossal leap from the high ground of responsible stewardship into a swamp of reckless devotion.

'What're you doing?' she demanded again.

He answered this time, but his reply was neither reassuring nor informative: 'I don't know.'

She sensed a quality in his demeanor that was reminiscent of her desperate state of mind each time she found herself in the thrall of a mirage. Alarmed by the prospect of being driven at high speed by a man distracted by hallucinations or worse, she said, 'Slow down, for God's sake. Where are you going?'

Accelerating, he said, 'West. Somewhere west. A place. Some place.'

'Why?'

'I feel the pull.'

'The pull of what?'

'The west. I don't know. I don't know what or where.'

'Then why are you going anywhere at all?'

As if he were the simplest of men for whom this conversation had taken a philosophical turn no less beyond his comprehension than the arcane discoveries of molecular biology, Dylan rolled his gaze toward her, revealing as much white of the eyes as does a dog cringing in bewilderment from harsh words that it can't understand. 'It just… feels right.'

'What feels right?'

'Going this direction, going west again.'

'Aren't we driving straight back into trouble?'

'Yeah, probably, I think so.'

'Then pull over, stop.'

'Can't.' An instant sweat slicked his face. 'Can't.'

'Why?'

'Frankenstein. The needle. The stuff. It's started. Something's happening to me.'

'What something?'

'Some weird shit.'

In the backseat, Shepherd said, 'Manure.'

Weird manure indeed.

As though he were fleeing from a fast-moving fire or outrunning an avalanche of tumbling rock and ice and snow, Dylan O'Conner was flogged by a sense of urgency so intense that his heart jumped like that of a rabbit running in the shadow of a wolf. He had never suffered feelings of persecution and had never taken methamphetamine, but he supposed this must be how a man with paranoid delusions would feel if he mainlined a near-lethal dose of liquid speed.

'I'm jacked up,' he told Jilly, pressing the accelerator, 'and I don't know why, and I can't get down.'

God alone knew what she made of that. Dylan himself wasn't sure what he'd been trying to convey.

In fact, he didn't feel that he was running from danger, but that he was being drawn inexorably toward something by the world's largest electromagnet, which pulled him by the iron in his blood. His sense of urgency was matched by an irresistible compulsion to move.

The urgency had no apparent cause, and the compulsion related to no specific object. He simply needed to go west, and he felt constrained to race after the setting moon with all possible haste.

Instinct, he told Jilly. Something in his blood that said go, something in his bones that said hurry, a race-memory voice speaking through his genes, a voice that he knew he dared not ignore, because if he resisted its message, something terrible would happen.

'Terrible?' she asked. 'What?'

He didn't know, he only felt, as a stalked antelope feels the cheetah lurking a hundred yards away behind a screen of tall grass, and as a parched cheetah senses the presence of a water hole miles away across the veldt.

Trying to explain himself, he'd let up on the accelerator. The speedometer needle quivered at 85. He pumped it toward 90.

In this traffic, on this highway, in this vehicle, driving at ninety miles per hour wasn't only illegal and imprudent, but foolish, and worse than foolish – moronic.

He wasn't able either to shame or argue himself into reacting responsibly to the risk. Shep's life and Jilly's, as well as his own, were jeopardized by this monomaniacal determination to move and to move fast, faster, always west, west. On another night or even at an earlier hour this night, the mere recognition of his accountability for their safety would have caused Dylan to slow down, but now all moral considerations and even his survival instinct were overruled by this feverish compulsion.

Macks and Peterbilts, sedans, coupes, SUVs, pickups, vans, auto carriers, motor homes, tanker trucks raced westward, weaving back and forth from lane to lane, and without once slowing, Dylan plunged the Expedition through the gaps in traffic as expertly as an eagle-eyed tailor speed-threading a long series of needles.

As the speedometer indicated 92, his fear of crashing into another vehicle influenced him less than did the pure animal need to move. When it eased past 93, he grew concerned about the waves of vibrations that rattled the chassis, but not concerned enough to be able to cut their speed.

This urgent necessity, this sense that he must drive hard or die, exceeded mere compulsion, possessed him so fully as to be no less than an obsession, until with every rushing breath he heard within his mind the dire admonition You're running out of time, and heard with every racing heartbeat the exhortation Faster!

Encountering chuckholes, cracks, and patches in the pavement, the tires stuttered as hard as rapping hammers, and Dylan worried about the consequences of a blowout at this lightning pace, but he pressed the Expedition to 96, taxing the shock absorbers, torturing the springs, onward to 97, with engine screaming and wind of their own manufacture shrieking at the windows, to 98, between bracketing big rigs, around a sleek Jaguar with a cruise-missile whoosh that elicited a disapproving blast of the sports car's horn, to 99.