“I will,” said Jimmy. “It had better be good.”

He did not interrupt the Commander again, and made no comment when Norton had finished. Yes, it made sense, and was so absurdly simple that it would take a genius to think of it. And, perhaps, someone who did not expect to do it himself…

Jimmy had never tried high-diving, or made a delayed parachute drop, which would have given him some psychological preparation for this feat. One could tell a man that it was perfectly safe to walk a plank across an abyss—yet even if the structural calculations were impeccable, he might still be unable to do it. Now Jimmy understood why the Commander had been so evasive about the details of the rescue. He had been given no time to brood, or to think of objections.

“I don’t want to hurry you,” said Norton’s persuasive voice from half a kilometre below. “But the sooner the better.” Jimmy looked at his precious souvenir, the only flower in Rama. He wrapped it very carefully in his grimy handkerchief, knotted the fabric, and tossed it over the edge of the cliff.

It fluttered down with reassuring slowness, but it also took a very long time getting smaller, and smaller, and smaller, until he could no longer see it. But then Resolution surged forward, and he knew that it had been spotted.

“Beautiful!” exclaimed the Commander enthusiastically. “I’m sure they’ll name it after you. OK—we’re waiting…”

Jimmy stripped off his shirt—the only upper garment anyone ever wore in this now-tropical climate—and stretched it thoughtfully. Several times on his trek he had risked his life.

For the last time, he looked back at the hollow world he alone had explored, and the distant, ominous pinnacles of the Big and Little Horns. Then, grasping the shirt firmly with his right hand, he took a running jump as far out over the cliff as he could. Now there was no particular hurry; he had a full twenty seconds in which to enjoy the experience. But he did not waste any time, as the wind strengthened around him and Resolution slowly expanded in his field of view. Holding his shirt with both hands, he stretched his arms above his head, so that the rushing air filled the garment and blew it into a hollow tube.

As a parachute, it was hardly a success; the few kilometres an hour it subtracted from his speed was useful, but not vital. It was doing a much more important job—keeping his body vertical, so that he would arrow straight into the sea.

He still had the impression that he was not moving at all, but that the water below was rushing up towards him. Once he had committed himself, he had no sense of fear; indeed, he felt a certain indignation against the skipper for keeping him in the dark. Did he really think that he would be scared to jump, if he had to brood over it too long?

At the very last moment, he let go of his shirt, took a deep breath, and grabbed his mouth and nose with his hands. As he had been instructed, he stiffened his body into a rigid bar, and locked his feet together. He would enter the water as cleanly as a falling spear…

“It will be just the same,” the Commander had promised, “as stepping off a diving board on Earth. Nothing to it—if you make a good entry.”

“And if I don’t?” he had asked. “Then you’ll have to go back and try again.” Something slapped him across the feet—hard, but not viciously. A million slimy hands were tearing at his body; even though his eyes were tightly closed, he could tell that darkness was falling as he arrowed down into the depths of the Cylindrical Sea.

With all his strength, he started to swim upwards towards the fading light. He could not open his eyes for more than a single blink; the poisonous water felt like acid when he did so. He seemed to have been struggling for ages, and more than once he had a nightmare fear that he had lost his orientation and was really swimming downwards. Then he would risk another quick glimpse, and every time the light was stronger.

His eyes were still clenched tightly shut when he broke water. He gulped a precious mouthful of air, rolled over on his back, and looked around.

Resolution was heading towards him at top speed; within seconds, eager hands had grabbed him and dragged him aboard.

“Did you swallow any water?” was the Commander’s anxious question.

“I don’t think so.”

“Rinse out with this, anyway. That’s fine. How do you feel?”

“I’m not really sure. I’ll let you know in a minute. Oh… thanks, everybody.” The minute was barely up when Jimmy was only too sure how he felt.

“I’m going to be sick,” he confessed miserably. His rescuers were incredulous.

“In a dead calm—on a flat sea?” protested Sergeant Barnes, who seemed to regard Jimmy’s plight as a direct reflection on her skill.

“I’d hardly call it flat,” said the Commander, waving his arm around the band of water that circled the sky. “But don’t be ashamed—you may have swallowed some of that stuff. Get rid of it as quickly as you can.”

Jimmy was still straining, unheroically and unsuccessfully, when there was a sudden flicker of light in the sky behind them. All eyes turned towards the South Pole, and Jimmy instantly forgot his sickness. The Horns had started their firework display again.

There were the kilometre-long streamers of fire, dancing from the central spike to its smaller companions. Once again they began their stately rotation, as if invisible dancers were winding their ribbons around an electric maypole. But now they began to accelerate, moving faster and faster until they blurred into a flickering cone of light.

It was a spectacle more awe-inspiring than any they had yet seen here, and it brought with it a distant crackling roar which added to the impression of overwhelming power. The display lasted for about five minutes; then it stopped as abruptly as if someone had turned a switch.

“I’d like to know what the Rama Committee make of that,” Norton muttered to no one in particular. “Has anyone here got any theories?”

There was no time for an answer, because at that moment Hub Control called in great excitement.

“Resolution! Are you OK? Did you feel that?”

“Feel what?”

“We think it was an earthquake—it must have happened the minute those fireworks stopped.”

“Any damage?”

“I don’t think so. It wasn’t really violent but it shook us up a bit.”

“We felt nothing at all. But we wouldn’t, out here in the Sea.”

“Of course, silly of me. Anyway, everything seems quiet now… until next time.”

“Yes, until the next time,” Norton echoed.

The mystery of Rama was steadily growing; the more they discovered about it, the less they understood.

There was a sudden shout from the helm.

“Skipper—look—up there in the sky!”

Norton lifted his eyes, swiftly scanning the circuit of the Sea. He saw nothing, until his gaze had almost reached the zenith, and he was staring at the other side of the world.

“My God,” he whispered slowly, as he realized that the “next time” was already almost here.

A tidal wave was racing towards them, down the eternal curve of the Cylindrical Sea.