"It's only a meter thick at the top," she said. "Judging by the color, I'd guess it's made out of the same stuff as the wells and the corridor."

"That is, nothing," Farley said. "Patricia's spatial building blocks."

Heineman reduced speed to a few hundred kilometers an hour and they glided through the hole. On the opposite side, the view of the corridor floor was crystal clear, unobstructed by atmosphere. The floor was a chaotic mess of hundred-kilometer-long gouges, black marks and broad strips of revealed bronze corridor surface. The instruments confirmed their suspicions.

"No atmosphere," Farley said. "The wall's a plug." Heineman decelerated until they came to a stop two thousand kilometers past the wall, now reduced in size to a tiny patch in the corridor's merciless perspective. "What'll it be?" he asked.

"We slide back and find a well circuit," Lanier said, "just like we planned. We check that out, then we proceed—and we don't waste time. Research is really secondary."

"Yessir," Heineman said. He swung the V/STOL around on the tuberider to face the opposite direction. "Hang on; full reverse coming up."

Four hundred kilometers south of the wall, they located a circuit of wells and slowed to prepare the V/STOL for its descent. All loose objects were made fast while Heineman unlocked the aircraft from the tuberider. With a gentle nudge of the attitude jets, they eased away from the singularity. Heineman oriented the craft with its nose toward the corridor floor.

Unlike in the asteroid chambers, where some sort of push was required to move away from the axis, the V/STOL began a slow, accelerating descent immediately, repelled by the singularity—or attracted by the floor, whichever way they cared to think of it. After falling four kilometers, Heineman kicked in the rocket engine for three short bursts and pointed the plane's nose north. "I wouldn't land this way in a chamber," he said, "but it's the best tactic in the corridor. We won't hit the atmosphere on a spiral course here. So I'm going to take advantage of a long glide down. Garry, take hold of your controls and get the feel of what I'm doing."

Lanier gripped the wheel and felt Heineman's motions as he pulled the nose up. A rippling series of shudders announced atmospheric buffeting; outside the walls a whimpering whine began to decrease in pitch and increase in loudness. Heineman brought down flaps to decrease their airspeed and gently swung the V/STOL to the right, lowering the nose and deploying the prop blades from their receptacles in the engine nacelles. The smooth, beautiful roar of the twin turboprops made him smile like a little boy. "Ladies and gents," he said, "we are now an airplane. Garry, like to take it down?"

"My pleasure," Lanier said. "Passengers will please keep their seatbelts on."

"Aye-aye," Carrolson said.

"That was fun. Let's do it again," Farley called forward.