The omniscope showed a snowstorm.

"Bad weather down there, then," said Ridcully.

"No, it's thaumic interference," said Ponder. "They're passing under the elephants. We'll get a lot more of it, I'm afraid."

"Did they really say "Ankh-Morpork, we have an orangutan"?" said the Dean.

"The Librarian must have got on board somehow," said Ponder. "You know what he's like for finding odd corners to sleep in. And that, I'm afraid, explains about the weight and the air. Er . . . I have to tell you that I'm not sure that they have enough time or power to get back on to the Disc now."

"What do you mean, you're not sure?" said Lord Vetinari.

"Er . . . I mean I am sure but, er, no one likes bad news all at once, sir."

Lord Vetinari looked at the big spell that dominated the cabin. It floated in the air: the whole world, sketched in glowing lines and, dropping from one glittering edge, a small curving line. As he watched it lengthened slightly.

"They can't just turn around and come back?" he said.

"No, sir. It doesn't work like that."

"Can they throw the Librarian out?"

The wizards looked shocked.

"No, sir," said Ponder. "That would be murder, sir."

"Yes, but they may save the world. One ape dies, one world lives. You do not need to be a rocket wizard to work that out, surely?"

"You can't ask them to make a decision like that, sir!"

"Really? I make decisions like that every day," said Lord Vetinari. "Oh, very well. What are they short of?"

"Air and dragon power, sir."

"If they chop up the orangutan and feed him to the dragons, won't that kill two birds with one stone?"

The sudden iciness told Lord Vetinari that once again he hadn't taken his audience with him. He sighed.

"They need dragon flame to . . . ?" he said.

"To bring their ringpath over the Disc, sir. They have to fire the dragons at the right time."

Vetinari looked at the magical orrery again. "And now . . . ?"

"I'm not quite sure, sir. They may crash into the Disc, or they may shoot straight out into endless space."

"And they need air . . ."

"Yes, sir."

Vetinari's arm moved through the outline of the world and a long forefinger pointed.

"Is there any air here?" he said.