He had had it built after inheriting some money from a deceased aunt. His wife had wanted a new car, or investment property. The construction drove a wedge into the crack of a failing marriage.

Ostrowski bypassed the door to the house proper and went to the entrance at the northeast end of the conservatory. The bell jar had become an onerous weight; it massed about fifteen pounds, and he had carried it for almost half a mile.

At the door, he realized he needed two hands. He painfully set the jar down on the steps, shook out his arms to unkink them, and yanked his keys free from his jacket pocket.

Inside the conservatory the air was, as always, humid. Normally Ostrowski moved slowly in it, pausing here to check for rot or there to peer at seedlings in the propagating case. Today, without looking at any of his plants he lumbered directly to the switch that overrode the automatic functioning of the ventilator panels along the ridge of the roof, and jabbed it. The vents, open as usual at this time of day, closed.

He checked his workbench. Plenty of room for the bell jar. He stared down the length of the aisle to the open door. Was he taking a risk by bringing the cloud indoors?

"Don't know what else I can do," he muttered, taking off his hat and wiping the perspiration from his brow with the sleeve of his suitcoat. "Can't keep a cloud in a jar. It'll have to replenish its vapor somehow, probably, I guess... I don't know."

What, however, of its lightning? Would that harm his other plants?

He eyed the vents. They were covered with cheesecloth to prevent bugs from getting in. Eventually he'd have to open them to provide air for the plants. Might the cloud diffuse through the cloth? He cracked his knuckles, then went to fetch the jar.

There was no question of snatching off the bell and ducking for cover; the thick glass was too heavy and awkward for that. Taking a deep breath, he lifted it off the base.

The cloud, curdling in on itself like murky water, remained floating over the base for a moment, then bobbed up like a child's balloon, pausing inches below the ceiling.

Over the next hour, it made several very slow circuits of the conservatory in response to the weak air currents. Every so often, it flickered, like a candle in a bag. Ostrowski found himself wondering if it could somehow be made to rain on his plants. It didn't look like it could contain much water.

He realized he was famished, and went in to slap together a quick meal of sandwiches and diet soda. With this, and the encyclopedia volumes containing WEATHER, CLOUDS and METEOROLOGY, he returned to the conservatory and settled in to read.

The conservatory was a jungle under the full moon. The only other illumination came from a small lamp he'd lit in the living room and angled through the French doors for reading light.

The cloud hung near the top of the conservatory, just below the roof, above the Norfolk Island pines and the suspended English ivy.

His acquisition was apparently a typical thundercloud. Typical, except for its amazing miniature condition. According to the books, thunderclouds normally weighed many thousands of tons. He glanced uneasily up at his "guest," hovering above the saxifrage, then resumed reading.

Presently he got up to go to the bathroom. On his return, and without really thinking about it, he opened the French doors wide. The cloud, floating nearby, almost slipped into the house, giving him a bad scare.

As the night wore on, he gradually lost his apprehension while watching the little cloud drifting among his plants. He noticed that it never came closer than three or four inches to anything. It probably would not, therefore, be able to sail out through the ventilator cloth. The doors were another story. Ostrowski knew he'd have to be careful with his comings and goings.

Around midnight, long past his usual bedtime, he closed his eyes for a few moments to rest them, and fell toward a doze. A vague thought of his abandoned car jerked him awake. He sat blinking. Well, he would get the car in the morning. It was off the road, safe for the night. He looked around for the cloud. It wasn't easy to see at night among the plant growth unless one knew exactly where to look, or unless it emitted one of its tiny sparks of lightning.

Then he saw it, above the gardenia tree near the star jasmine vine. Here the moonlight poured through the Plexiglas, golden from the UV-reducing tint. The cloud looked like brassy smog.

Ostrowski's buttocks ached and his eyes were scratchy and watery. He decided to go to bed. Wearily he stood.

Suddenly the cloud was above him, scant inches over his head like a ghost hat. He froze. The cloud made no further move. Carefully and very slowly, he edged toward the French doors. The cloud paced him, remaining immediately over his bald spot. His eyes stung with the strain of trying to look up through his skull: he didn't dare raise his face for fear of lightning.

Sweat trickled down his double chin. The cloud would clearly trail him into the house, if he let it. He chewed the soft point of his upper lip until it began to fray. He was going to have to make a break for it. He knew that if he paused to weigh his chances his nerve would abandon him. With a half-snort, half-whimper he dove for the door, pushed it open, fell through and spun back into it. There was a crack of glass. His breath jammed in his throat, but the pane held.

The cloud floated beyond the door above the place he had just vacated.

Shakily he inspected the cracked pane. Replacing it would be a trivial job. In dull relief, he turned to switch off the reading lamp.

Snap! A tiny bolt of lightning splattered on the French door.