Rincewind found that looking ahead meant that he would have to turn and find out what a sea troll actually looked like, and he wasn’t sure he wanted to do that yet. He looked at the Rimbow instead. It hung in the mists a few lengths beyond the edge of the world, appearing only at morning and evening when the light of the Disc’s little orbiting sun shone past the massive bulk of Great A’tuin the World Turtle and struck the Disc’s magical field at exactly the right angle.

A double rainbow corruscated into being. Close into the lip of the Rimfall were the seven lesser colours, sparkling and dancing in the spray of the dying seas.

But they were pale in comparison to the wider band that floated beyond them, not deigning to share the same spectrum. It was the King Colour, of which all the lesser colours are merely partial and wishy-washy reflections. It was octarine, the colour of magic. It was alive and glowing and vibrant and it was the undisputed pigment of the imagination, because wherever it appeared it was a sign that mere matter was a servant of the powers of the magical mind. It was enchantment itself. But Rincewind always thought it looked a sort of greenish-purple.

After a while a small speck on the rim of the world resolved itself into a eyot or crag, so perilously perched that the waters of the fall swirled around it at the start of their long drop. A driftwood shanty had been built on it, and Rincewind saw that the top rope of the Circumfence climbed over the rocky island on a number of iron stakes and actually passed through the shack by a small round window. He learned later that this was so that the troll could be alerted to the arrival of any salvage on his stretch of the Circumfence by means of a series of small bronze bells, balanced delicately on on the rope.

A floating stockade had been built out of rough timber on the hubward side of the island. It contained one or two hulks and quite a large amount of floating wood in the form of planks, baulks and even whole natural tree trunks, some still sporting green leaves. This close to the Edge the disc’s magical field was so intense that a hazy corona flickered across everything as raw illusion spontaneously discharged itself.

With a last few squeaky jerks the boat slid up against a small driftwood jetty. As it grounded itself and formed a circuit Rincewind felt all the familiar sensations of a huge occult aura - oily, bluish-tasting, and smelling of tin. All around them pure, unfocused magic was sleeting soundlessly into the world.

The wizard and Twoflower scrambled onto the planking and for the first time Rincewind saw the troll.

It wasn’t half so dreadful as he had imagined. Umm, said his imagination after a while.

It wasn’t that the troll was horrifying. Instead of the rotting, betentacled monstrosity he had been expecting Rincewind found himself looking at a rather squat but not particularly ugly old man who would quite easily have passed for normal on any city street, always provided that other people on the street were used to seeing old men who were apparently composed of water and very little else. It was as if the ocean had decided to create life without going through all that tedious business of evolution, and had simply formed a part of itself into a biped and sent it walking squishily up the beach. The troll was a pleasant translucent blue colour. As Rincewind stared a small shoal of silver fish flashed across its chest.

“It’s rude to stare,” said the troll. Its mouth opened with a little crest of foam, and shut again in exactly the same way that water closes over a stone.”

“Is it? Why?” asked Rincewind. How does he hold himself together, his mind screamed at him. Why doesn’t he spill?

“If you will follow me to my house I will find you food and a change of clothing,” said the troll solemnly. He set off over the rocks without turning to see if they would follow him. After all, where else could they go? It was getting dark, and a chilly damp breeze was blowing over the edge of the world. Already the transient Rimbow had faded and the mists above the waterfall were beginning to thin.

“Come on,” said Rincewind, grabbing Twoflower’s elbow. But the tourist didn’t appear to want to move.

“Come on,” the wizard repeated.

“When it gets really dark, do you think we’ll be able to look down and see Great A’tuin the World Turtle?” asked Twoflower, staring at the rolling clouds.

“I hope not,” said Rincewind, “I really do. Now let’s go, shall we?”

Twoflower followed him reluctantly into the shack. The troll had lit a couple of lamps and was sitting comfortably in a rocking chair. He got to his feet as they entered and poured two cups of a green liquid from a tall pitcher. In the dim light he appeared to phosphoresce, in the manner of warm seas on velvety summer nights. Just to add a baroque gloss to Rincewind’s dull terror he seemed to be several inches taller, too.

Most of the furniture in the room appeared to be boxes.

“Uh. Really great place you’ve got here,” said Rincewind. “Ethnic.”

He reached for a cup and looked at the green pool shimmering inside it. It’d better be drinkable, he thought. Because I’m going to drink it. He swallowed.

It was the same stuff Twoflower had given him in the rowing boat but, at the time, his mind had ignored it because there were more pressing matters. Now it had the leisure to savour the taste.

Rincewind’s mouth twisted. He whimpered a little. One of his legs came up convulsively and caught him painfully in the chest.

Twoflower swirled his own drink thoughtfully while he considered the flavour.

“Ghlen Livid,” he said. “The fermented vul nut drink they freeze-distil in my home country. A certain smokey quality… Piquant. From the western plantations in, ah, Rehigreed Province, yes? Next year’s harvest, I fancy, from the colour. May I ask how you came by it?”

(Plants on the disc, while including the categories known commonly as annuals, which were sown this year to come up later this year, rieanuals, sown this year to grow next year, and perennials, sown this year to grow until further notice, also included a few rare re-annuals which, because of an unusual four-dimensional twist in their genes, could be planted this year to come up last year. The Vul nut vine was particularly exceptional in that it could flourish as many as eight years prior to its seed actually being sown. Vul nut wine was reputed to give certain drinkers an insight into the future which was, from the nut’s point of view, the past. Strange but true.)

“All things drift into the Circumfence in time,” said the troll, gnomically, gently rocking in his chair. “My job is to recover the flotsam. Timber, of course, and ships. Barrels of wine. Bales of cloth. You.”

Light dawned inside Rincewind’s head.

“It’s a net, isn’t it? You’ve got a net right on the edge of the Sea!”

“The Circumfence,” nodded the troll. Ripples radiating across his chest.

Rincewind looked out into the phosphorescent darkness that surrounded the island, and grinned inanely.

“Of course,” he said. “Amazing! You could sink piles and attach it to reefs and - good grief! The net would have to be very strong.”

“It is,” said Tethis.

“It could be extended for a couple of miles, if you found enough rocks and things,” said the wizard.

“Ten thousands of miles. I just patrol this length.”

“That’s a third of the way around the disc!”

Tethis sloshed a little as he nodded again. While the two men helped themselves to some more of the green wine, he told them about the Circumfence, the great effort that had been made to build it, and the ancient and wise Kingdom of Krull which had constructed it several centuries before, and the seven navies that patrolled it constantly to keep it in repair and bring its salvage back to Krull, and the manner in which Krull had become a land of leisure ruled by the most learned seekers after knowledge, and the way in which they sought constantly to understand in every possible particular the wondrous complexity of the universe, and the way in which sailors marooned on the Circumfence were turned into slaves, and usually had their tongues cut out. After some interjections at this point he spoke, in a friendly way, on the futility of force, the impossibility of escaping from the island except by boat to one of the other three hundred and eighty isles that lay between the island and Krull itself, or by leaping over the Edge and the high merit of muteness in comparison to for example, death.

There was a pause. The muted night-roar of the Rimfall only served to give the silence a heavier texture.

The rocking chair started to creak again. Tethis seemed to have grown alarmingly during the monologue.

“There is nothing personal in all this,” he added. “I, too, am a slave. If you try to overpower me I shall have to kill you, of course, but I won’t take any particular pleasure in it.”

Rincewind looked at the shimmering fists that rested lightly in the troll’s lap. He suspected they could strike with all the force of a tsunami.

“I don’t think you understand,” explained Twoflower. “I am a citizen of the Golden Empire. I’m sure Krull would not wish to incur the displeasure of the Emperor.”

“How will the emperor know?” asked the troll.

“Do you think you’re the first person from the Empire who has ended up on the Circumfence?”

“I won’t be a slave,” shouted Rincewind. “I’d - I’d jump over the Edge first!” He was amazed at the sound in his own voice.

“Would you, though?” asked the troll. The rocking chair flicked back against the wall and one blue arm caught the wizard around the waist. A moment later the troll was striding out of the shack with Rincewind gripped carelessly in one fist.

He did not stop until he came to the Rimward edge of the island. Rincewind squealed.

“Stop that or I really will throw you over the edge,” snapped the troll. “I’m holding you, aren’t I? Look.”

Rincewind looked.

In front of him was a soft black night whose mist-muted stars glowed peacefully. But his eyes turned downwards, drawn by some irresistible fascination.

It was midnight on the Disc and so, therefore, the sun was far, far below, swinging slowly under Great A’Tuin’s vast and frosty plastron. Rincewind tried a last attempt to fix his gaze on the tips of his boots, which were protruding over the rim of the rock, but the sheer drop wrenched it away.

On either side of him two glittering curtains of water hurtled towards infinity as the sea swept around the island on its way to the long fall. A hundred yards below the wizard the largest sea salmon he had ever seen flicked itself out of the foam in a wild, jerky and ultimately hopeless leap. Then it fell back, over and over, in the golden underworld light.

Huge shadows grew out of that light like pillars supporting the roof of the universe. Hundreds of miles below him the wizard made out the shape of something, the edge of something-

Like those curious little pictures where the silhouette of an ornate glass suddenly becomes the outline of two faces, the scene beneath him flipped into a whole, new, terrifying perspective. Because down there was the head of an elephant as big as a reasonably-sized continent. One mighty tusk cut like a mountain against the golden light, trailing a widening shadow towards the stars. The head was slightly tilted, and a huge ruby eye might almost have been a red super-giant that had managed to shine at noonday.