Only during that incredibly tiny moment of time was the tunnel open. I had to step into the crystal latticework, through the searing hot wall of the chamber, at precisely the exact moment — or not at all.

I got to my feet and forced myself close to the wall. The heat was enough to singe the hair of my eyebrows and the backs of my hands. I kept my eyes closed, picturing with one side of my brain the crystal pathway itself, while simultaneously calculating with the other side of my brain the precise moment when the lattice would be open for me to step through.

With my eyes still closed I took a step forward. I felt an instant of roasting heat, then cold beyond the most frigid ice fields of Antarctica. Then…

I opened my eyes. I stood in the shadowy cellar of the STOPP house. For the first time in what seemed like years, I let out my breath and took in a double lungful of sweet, cool air.

I found a back door to the cellar and stepped out into the cold night. It felt wonderful. An alley led between the house and its next-door neighbor to the street. My rented car was still there, adorned with a yellow parking ticket affixed to its windshield wiper. I stuffed the ticket into my jacket pocket and got behind the wheel, glad that no one had towed the car away or stolen it.

It took me ten minutes to get back to the fusion lab. Once in the deserted lobby of the building, I phoned for Tom Dempsey, Mangino the security chief, and the lab’s director of research. It was close to midnight, but the tone of my voice must have convinced them that something important was happening. I got no arguments from any of them, although the phone’s computer had to try three different numbers before it located Dr. Wilson, the research director.

They all arrived in the lab within a half-hour — thirty minutes during which I checked personally with every security guard on duty. No one had reported the slightest problem. They were on constant patrol around the laboratory, inside and out, and everything appeared to be quite normal.

Dr. Wilson was a lanky, ruddy-faced, tousle-haired Englishman who spoke softly and seemed totally unflappable. He arrived first. As I was explaining that somebody would try to detonate the fusion reactor — and he smiled tolerantly at the ridiculous idea — Dempsey and the security chief came into the lobby together. Dempsey looked more puzzled than upset. His dark hair was an uncombed, tangled mop; he must have been asleep when I called and pulled his clothes on helter-skelter. Mangino was definitely angry. His narrow brown eyes snapped at me.

“This is a lot of hysterical nonsense,” he growled, when I explained my fears. I didn’t tell them about Ormazd and Ahriman, of course, nor about the underground chamber I’d just escaped from. It was enough to convince them that a real danger existed. I didn’t want them to bundle me off to a psychiatric ward.

Dr. Wilson tried to tell me that the reactor simply could not explode. I let him talk; the longer he explained, the longer we stayed on the scene, available to counter Ahriman’s move.

“There simply is not enough deuterium in the reactor at any given moment to allow an explosion,” Wilson repeated in a his soft, friendly voice. He sat slouched on one of the plastic couches that decorated the lab’s lobby. I stood by the receptionist’s desk. Dempsey had stretched out on another couch and apparently had gone back to sleep. Mangino was behind the desk, checking out his security patrols on the picture phone.

“But suppose,” I stalled for more time, “there was a way to boost the power of the lasers…”

“They’d burn out in a minute,” Wilson said. “We’re running them at top capacity now.”

“…and an extra amount of deuterium was put into the reaction chamber.”

Wilsons hook his head, and a mass of sandy hair flopped down over his eyes. Pushing it back with one hand, he told me, “That simply cannot happen. There are fail-safe circuits to prevent it. And even if it did, all that would happen is that you would get a mild little poof of a detonation — not a hydrogen bomb.”

“What about a lithium bomb?” I asked.

For the first time, his eyebrows knit worriedly. “What do you mean?”

“If things worked out the right way, couldn’t the deuterium detonation trigger the lithium in the shielding around the reaction chamber?”

“No, no. That would be impos—” He checked himself, hesitated, then said slowly, “That would be very unlikely. Very unlikely. I’d have to work out the calculations, of course, but the chances against that must be…”

“Twenty-four, report.” Mangino’s razor-sharp voice sliced into our conversation.

I turned and looked at the security chief. He was frowning angrily into the phone’s picture screen. “Dammit, Twenty-four, answer me!”

He looked up at me, as if I were responsible. “One of the guards outside doesn’t respond. He’s supposed to be patrolling the area around the loading dock.”

“The loading dock!” Wilson shot to his feet. I could see that he had started to tremble.

Mangino held up a hand. “Don’t get excited, now. I’ve got the area on one of the outside TV cameras. Everything looks normal. Just no sign of the guard. He might be taking a leak or something.”

I went around the desk and peered at the TV screen. The loading bay was brightly lit. There were no cars or trucks anywhere in sight. All seemed quiet and calm.

“Let’s take a walk down there anyway,” I said.

We roused Dempsey and told him to stand guard over the phones and TV screens. He rubbed his eyes sleepily but nodded okay. Then Dr. Wilson, Mangino and I hurried down the building’s central corridor toward the loading dock. Mangino reached inside his coat and pulled out a slim, flat, dead-black pistol. He flicked the safety off and then slipped it into his jacket pocket.

Lights turned on automatically ahead of us as we hustled along the corridor, and switched off behind us. The loading bay was a miniature warehouse: stacks of cardboard cartons, steel drums, packing cases, strange-looking equipment wrapped in clear plastic.

“You could hide a platoon of men in here,” Mangino grumbled.

“But everything seems to be in order,” Wilson said, glancing around. I started to agree, but felt the slightest trace of a breeze on my face. It came from the direction of the loading dock doors, big metal roll-up doors that were closed and locked tight. Or were they? I walked slowly toward the hangar-like doors and saw that a man-sized doorway had been cut into one of them. A person could slip in or out without needing to raise the entire rig. This smaller door was windowless. And shut. I reached for its handle.

“It’s locked,” Mangino said. “Electronic time lock. If anybody tries to tamper with it…”

I touched the handle and the door swung open effortlessly. Mangino gaped.

Kneeling, I saw that the area around the edge of the lock had been bent slightly, as if massive hands had pried it open, bending the metal until it yielded. I had felt the stray breeze through the bent area.

“Why didn’t the alarm go off?” Mangino wondered aloud.

“Never mind that,” I said. “He’s inside the lab! Quick; we don’t have a second to lose!”

We ran to the fusion reactor area,Wilson protesting all the way that no one could tamper with the lasers or the reactor to cause an explosion.

The doors to the laser control room had been pulled off their hinges. A quick look inside showed that no one was in there. The control boards seemed untouched. While Wilson inspected them, Mangino yelled into his palm-sized radio, “All security guards converge on the reactor area. Apprehend anyone you see. Shoot if they resist. Call the local police and the F.B.I. at once!”

We entered the big double doors that led to the long, cement-walled room where the lasers were housed. Again the overhead lights snapped on automatically as we crossed the doorway.