"You think so?" Joe asked.

"There's the possibility," Santa said.

"Doesn't radiation cause tissue cancer, blood cancer, bone cancer and immediate or lingering death?" Joe asked.

"Theoretically," Santa granted. "Plutonium's got a clean bill of health so far."

"It's only been on earth five months," Joe pointed out. "Ray and I made the first run."

"In the fucking snow," Ray said.

Ahead, the repair truck fishtailed from side to side over loose rocks.

"But in three weeks," Santa said, "there'll be hundreds of GIs at Trinity and they'll all be wondering why they're there and what they're doing, and they'll be talking to MPs who will overhear scientists talking, that's human nature, and there will be some anxiety, because GIs are not scientists, about being in proximity to a nuclear explosion. You see, there won't be a radiation problem, but there may be a psychological problem. Even though they know the Army would not put soldiers in a situation that was not entirely safe. After all, here's a bomb that's supposed to blow up a city with just a few pounds of refined ore. I was wondering how you two feel about that."

"The city part's okay," Ray said. "Don't ask us," Joe said.

"But you might feel anxiety," Santa suggested. "You two are the ones transporting that refined ore. Even though you know you're surrounded and protected by dedicated officers, you might feel anxiety."

"You don't feel any anxiety?" Joe asked. "None," Santa assured Joe. "Not a bit." Joe glanced back. Behind Santa, the canister floated securely in the web of straps and steel frame.

"No dedicated officers in this fucking wagon that I notice," Ray said.

"Then you, Sergeant Stingo, do admit to ambivalence."

"It was an ambulance," Ray said, "now they made it into this wagon."

"No, I mean ambivalence."

"It was. It's not now."

Ray stirred. All the paranoia that had been floating free up till now was starting to come together, to find its target after miles, although it hadn't coalesced yet, hadn't absolutely fixed. He twisted in his seat the better to regard Santa.

"Ambivalence, Sergeant. Wanting two things at the same time."

"Yeah," Ray muttered. "Two ambulances. We could bring twice as much."

"Anyway," Santa persevered, seeing no warning sign in the red eyes staring at him, "I asked myself, how can I treat a problem when I know nothing about it? How can we prepare for the possible mass emotional crises of the test site without seeing at least some enlisted men now in close proximity to hazardous radioactive material?"

"That's why we're here?" Ray asked.

"Because only you and Sergeant Pena actually know what the cargo is. The regular drivers and even the security officers only know that it's vital to the war effort."

"We're here because of you?" Ray asked.

"That's what I was just saying."

"We're here because of you?" Ray wanted to be sure.

"That's what I said I said."

"You?" Ray's eyes jerked back to the road when Joe hit a rabbit. His fingers twisted the handgrip of the Tommy gun.

"Because of me," Santa said with good-humoured firmness.

Joe could tell that Ray intended to turn and kill Santa as soon as he dared take his eyes from the road, but the tarmac now deteriorated to raw dirt. Last summer a Colorado Highways truck had spread oil on the road as a thin binder, but a winter in the Rockies had passed and the little oil that remained had become patches of dark slick between the long stretches of ice slick on a route that plunged at twenty degrees down the mountain side. Staying on the road would demand all of Ray's concentration even as a passenger. Even if Joe wanted to stop and take the gun from Ray, the sedan behind would hit them and pitch them over the edge of the road into the darkness that lay like a sea around them.

Santa seemed totally unconscious of the road, the mountains, the dark, as if danger and natural phenomena lay in Joe's area of expertise. Occasionally he commented on the effect of moonlight on a snowy peak, or the glint of a river a thousand feet below. Otherwise he behaved as if Joe had chosen a mildly diverting route.

"You!"

Ray tried to snatch his eyes from the road and kill Santa, but erosion had carved away the outer lane and the brake lights ahead blinked frantically, demanding his attention.

"Please take my word for it, Sergeant." There was movement behind Joe and the tang of pipe tobacco. "Mind if I smoke, men?" A flame glowed for a moment. Joe thought if he looked back there might be a blanket and a dog on Santa's lap. "The three of us are like Helios, bearing the sun across the sky. A new sun, of course. Just as we call the moon when we can't see it a new moon. There is an enormous synchroniesty building towards Trinity, a psychic tension. You men feel it, I can sense it."

"You want to sense something?"

Ray started to turn the Tommy gun, but a rock slide had poured over a hairpin bend in the road and Joe had to brake and turn without locking wheels.

"That's why I expect our problems at Trinity will be largely psychological." There was a rustle of paper. "Do you mind if I ask a few questions?"

Joe downshifted. The ambulance slid over stones to the edge of the road. Larger rocks bounced in front and rang off the crankcase underneath.

"Sergeant Stingo, if you heard that you were in close proximity to radioactive material, would you feel comfortable, concerned, a little anxious, very anxious?"

"Shit," Joe said.

The red tail-lights of the truck in front swung wildly.

"Boulder," Joe said.

It was the size of a doghouse and in the middle of the road. The truck cleared it on the right and slammed into the rock wall, scraping sparks off granite. Joe headed for the same space, skidding, holding the wheel steady. Ray and Tommy gun were pressed against the windshield. As the ambulance slipped past the boulder, Joe saw the truck ahead hit the wall again. Wrenches, jacks, tyres spilled from under the tarpaulin, bounced in the ambulance's headlights. As the truck stopped, nose into the wall, the ambulance slid through between the truck's tailboard and the road edge. The lead car had halted in the middle of the road. Joe swung in, braked and pulled the emergency brake at the same time, coming to rest against the car bumper only a second before the tail sedan rammed into the rear of the ambulance. A tyre wobbled out of the dark and past the headlights. Security officers ran up and down waving flashlights and Tommy guns. Even Ray was distracted.

A scream that was both feminine and unhuman erupted by Joe's ear, followed by a powerful, bell-like gong as Santa flew out of his seat head first and hit the ambulance roof. He seemed still to be suspended in mid-air when Joe looked past him to the rear of the ambulance and saw the empty steel square and eight slack straps. The plutonium canister had broken loose and rolled forward, glinting and warm, to nudge Santa's loafers and Argyle socks. The plutonium couldn't explode. Joe would have been happy to explain that to Santa, to reduce his psychic tension, given the chance. Santa dropped to the ambulance floor.

"Gee," said Ray.

"Orders are we don't stop for anything," the lieutenant in charge said when Joe pointed out the slumped figure of the analyst. "He's already in the ambulance, we'll leave him there."

"He's out cold, sir. He probably has concussion."

"Look, Sergeant, we're lucky no one in the truck was killed."

"What about this?" Joe pointed to the canister. "The strap hooks are broken."

"God, we can't have that thing rolling around. Somebody's going to have to hold it. We're losing time. Choose up, one of you has to take it. Or wedge it with something."

The truck, fender crumpled, was already weaving round the ambulance as the lieutenant ran off to the lead sedan. The convoy was re-assembling itself.