The wall ahead started to fall slowly back, but the CAT was coming up on it faster than it was crumpling. Horza gasped and tried to pull back; he heard Wubslin howl, as the vessel's nose hit the undamaged centre of the wall. The view on the main screen tilted as the ship rammed into the wall material. Then the nose came down, the Clear Air Turbulence quivered like an animal shaking water from its fur, and they were rocking and yawing into yet another Smallbay. It was totally empty. Horza gunned the engines a little more, took a couple of bursts with the laser at the next wall, then watched in amazement as this wall, instead of falling back like the last one, crashed down towards them like a vast castle drawbridge, slamming in one fiery piece onto the deck of the empty Smallbay. In a fury of steam and gas, a mountain of water appeared over the top of the collapsing wall and poured out in a huge wave towards the approaching ship.

Horza heard himself shouting. He rammed the motor controls full on and kept the laser fire button hard down.

The CAT leapt forward. It flashed over the surface of the cascading water, enough of the plasma heat smashing into its liquid surface to instantly fill all the space of Smallbays its passage had created with a boiling fog of steam. As the tide of water continued to pour from the flooded Smallbay and the CAT screeched above it, the air about the ship filled with superheated steam. The external pressure gauge went up too quickly for the eye to follow; the laser blasted even more vapour off the water in front, and with an explosion like the end of the world the next wall blew out ahead of the vessel — weakened by the laser and finally blasted away by the sheer pressure of steam. The Clear Air Turbulence shot out from the tunnel of linked Smallbays like a bullet from a gun.

Motors flaming, in the middle of a cloud of gas and steam which it quickly outdistanced, it roared into a canyon of air-filled space between towering walls of bay doors and opened accommodation sections, lighting up kilometres of wall and cloud, screaming with its three flame-filled throats, and seemingly pulling after it a tidal wave of water and a volcano-like cloud of steam, gas and smoke. The water fell, turning from a solid wave into something like heavy surf, then spray, then just rain and water vapour, following the huge flapping card of the bay door tumbling through the air. The CAT wrenched itself round, twisting and slewing through the air in an attempt to check its headlong rush towards the far wall of Smallbay doors facing it across that vast internal canyon. Then its motors flickered and went out. The Clear Air Turbulence started to fall.

Horza gunned the controls, but the fusion motors were dead. The screen showed the wall of doors to other bays on one side, then air and clouds, then the wall of bay doors on the other side. They were in a spin. Horza looked over at Wubslin as he fought with the controls. The engineer was staring at the main screen with a glazed expression on his face. "Wubslin!" Horza screamed. The fusion motors stayed dead-

"Aaah!" Wubslin seemed to have woken up to the fact that they were falling out of control; he leapt at the controls in front of him. "Just fly it!" he shouted. "I'll try the primers! Must have over-pressured the motors!"

Horza wrestled with the controls while Wubslin tried to restart the engines. On the screen, walls spun crazily about them and clouds beneath them were coming up fast — beneath them; really beneath them; a dead flat layer of clouds. Horza shook the controls again.

The nose motor burst into life, guttering wildly, sending the spinning craft careering off towards one side of the artificial cliff of bay doors and walls. Horza cut the motor out. He steered into the spin, using the craft's control surfaces rather than the motors, then he aimed the whole ship straight down and put his fingers on the laser buttons again. The clouds flashed up to meet the vessel. He closed his eyes and squeezed the laser controls.

The Ends of Invention was so huge it was built on three almost totally separate levels, each over three kilometres deep. They were pressure levels, there because otherwise the differential between the very bottom and the very top of the giant ship would have been the difference between standard sea level and a mountain top somewhere in the tropopause. As it was, there existed a three and a half thousand metre difference between the base and roof of each pressure level, making sudden journeys by traveltube from one to the other inadvisable. In the immense open cave that was the hollow centre of the GSV the pressure levels were marked by force fields, not anything material, so that craft could pass from one level to another without having to go outside the vessel, and it was towards one of those boundaries, marked by cloud, that the Clear Air Turbulence was falling.

Firing the laser did no good whatsoever, though Horza didn't know that at the time. It was a Vavatch computer, which had taken over the internal monitoring and control from the Culture's own Minds, which opened a hole in the force field to let the falling vessel through. It did so in the mistaken assumption that less damage would be caused to The Ends of Invention by letting the rogue vessel fall through than having it impact.

In the centre of a sudden maelstrom of air and cloud, in its own small hurricane, the CAT burst through from the thick air at the bottom of one pressure level and into the thin atmosphere at the top of the one below. A vortex of rag-clouded air blew out after it like an inverted explosion. Horza opened his eyes again and saw with relief the distant floor of the GSV's cavernous interior, and the climbing figures on the main fusion motors" monitor screens. He hit the engine throttles again, this time leaving the nose motor alone. The two main engines caught, shoving Horza back in his seat against the cloying hold of the restrainer fields. He pulled the nose of the diving craft up, watching the floor far below gradually disappear from view as it was replaced by the sight of another wall of opened bay doors. The doors were much larger than those of the Smallbays in the level they had just left, and the few craft Horza could see either nosing into or appearing out of the lit lengths of the huge hangars were full-size starships.

Horza watched the screen, piloting the Clear Air Turbulence exactly like an aircraft. They were travelling quickly along a vast corridor over a kilometre across, with the layer of clouds about fifteen hundred metres above them. Starships were moving slowly through the same space, a few on their own AG fields, most towed by light lifter tugs. Everything else was moving slowly and without a fuss; only the CAT disturbed the calm of the giant ship's interior, screaming through the air on twin swords of brilliant flame pulsing from white-hot plasma chambers. Another cliff-face of huge hangar doors faced them. Horza looked about him at the curve of main screen and pulled the CAT over on a long banking left turn, diving a little at the same time to head down an even broader canyon of space. They flashed over a slow-moving clipper being towed towards a distant open Mainbay, rocking the starship in their wake of superheated air. The wall of doors and opened entrances slanted towards them as Horza tightened the turn. Ahead, Horza could see what looked like a cloud of insects: hundreds of tiny black specks floating in the air.

Far beyond them, maybe five or six kilometres away, a thousand metre square of blackness, bordered with a slowly flashing strip of subdued white light, was the exit from The Ends of Invention. It was a straight run.

Horza sighed and felt his whole body relax. Unless they were intercepted, they had done it. With a little luck now, they might even get away from the Orbital itself. He gunned the engines, heading for the inky square in the distance.