Mr. Rundon and Mr. Oben walked past the Unseen University, the former skulking in the shadows cast by the building, which loomed impressively. He didn't like things that loomed, as they usually meant trouble for him. Mr. Oben loomed. Suddenly, the tall man stopped.

"We're being followed" he stated.

Mr. Rundon whimpered, and looked around nervously. If he hadn't been wearing it to protect his identity, he would have removed his hat and gnawed at the brim. He was that kind of person: the exact opposite of Mr. Oben, who couldn't help looking strangely like Death when not in full view. He had the odd habit of looming ominously at unexpected moments which was shared with that particular anthropomorphic personification.

"Who by?" asked Mr. Rundon.

"Whom" corrected Mr. Oben absently.

"What?"

"By whom, not who by." Mr. Oben looked at the Palace, and smiled. "Sergeant, or should I say, Lady Delphine Angua von Uberwald, daughter of Baron Wolfgang von Uberwald, from...where, Mr. Rundon?"

"Uberwald?" hazarded his assistant.

"Correct, Mr. Rundon. I see you have been paying attention. Who is her, ahem, romantic interest?"

"Captain Carrot Ironfoundersson, rightful king of Ankh-Morpork" answered Mr. Rundon.

This had been drummed into him so many times he could recite it in his sleep. Mr. Oben had forced him to learn the names and backgrounds of the most senior Watch officers.

"Good, Mr. Rundon. Arthur. Now, our little werewolf is going to get a shock, isn't she? Take this and drop it just in front of the entrance to that alley. Without, and this is important, without getting too close. Is that understood? Good."

He handed a little glass phial full of liquid to his companion.

"What's in there, Mr. Oben?"

"A mixture of aniseed oil and oil of scallatine, which has a rather...interesting effect on werewolves, as you will understand."

Mr. Rundon's expression showed that he didn't. Mr. Oben sighed.

"She has a very strong sense of smell, understand? And that phial contains some potent substances which, to a werewolf, will stink to high heaven. She'll be out of action for a few hours, maybe even a day, depends how close she gets to it. Now, deal with it now, and do not get caught!"

Vimes knocked on the Arch-chancellor's door, holding his helmet awkwardly under one arm.

"Come in!" commanded a rich voice.

He did so. The Arch-chancellor was sitting, no, lolling behind his desk, his feet resting on his desk. An expensive crossbow was cradled in one arm, and a glass of sherry was grasped in the other hand. The Bursar was standing in front of the desk, trembling with fear. That was his normal state, so Vimes didn't pay much attention to it. Ridcully looked up.

"Afternoon, Sam" he said cheerfully.

"Same to you, Mustrum."

Gesturing with his glass of sherry, he pointed Vimes towards a chair in front of his desk. The Bursar looked across at him, and smiled perplexedly.

"Do you happen to know where my spoon is? I know I had it yesterday" he remarked.

"Ignore him, poor fellow. He's on the dried frog pills again, gods help him. Want some dried frog pills, old chap?" queried Ridcully, raising his voice to speak to the Bursar.

"Frog pills?" replied the Bursar.

"In your pocket. The green things" explained the Arch-chancellor, miming patting his pockets down.

"Oh? Oh!"

The Bursar extracted a little box from his pocket and, with shaking fingers, opened it, produced two bright green pills and swallowed them. He gulped.

"Terribly sorry, sir; I'll come back later."

Bowing nervously to Vimes and Ridcully, the Bursar backed out, with a bemused expression on his round shiny face. As soon as the door clicked behind him, Ridcully turned to Vimes.

"What is it, Sam? Not meaning to be rude, but you understand you have no jurisdiction, as such, on University grounds."

"I have jurisdiction if the event is going to affect the city, Mustrum. My city."

"Go on" encouraged Ridcully, pouring Vimes a glass of water.

He took it gladly.

"Well. There is, or rather, was a book in your Library called the Octavo Explained" he began.

Ridcully frowned, and took a sip of his sherry.

"A book was stolen from the Library, which we later recovered. That book was on eldritch lace-making; we don't think that was the original intention of the thief. I went to the Library, and the Assistant Librarian showed me the gap in the shelf, which that book should have occupied. It was next to the Octavo Explained: I think that's what was meant to be stolen. The Librarian unlocked it for me, but the book was blank. Which begs the question: where is that book?"

The Arch-chancellor leant back in his chair and produced his pipe. He lit it, and studied the ceiling thoughtfully.

"Interesting. In that case, Sam, you may have access to our staff. Within reason. And I will supervise you, naturally. The Octavo. I would start with Mister Stibbons, personally. He might be able to use that thaumometer of his to find it. He's in the High Energy Magic Building. I recommend you go and fetch another officer, by the way. You may find it easier to, ahem, divide and conquer" he advised.

"Very well. I'll send a clacks to Pseudopolis Yard, if you don't mind" responded Vimes.

"Yes, yes, of course! If you give me the message, I can tell one of the bledlows to send it for you."

Vimes was about to protest, but then changed his mind.

"Thank you, yes."

He produced his cheap notebook and scribbled a message down onto a clean sheet, tore it out of the book, and handed it to Ridcully.

"The HEM is down that corridor, to the left. I strongly recommend you knock first: you never know what they're doing in there. Well, goodbye, Sam."

Vimes nodded, and went outside and down the corridor, towards the High Energy Magic Building. There was an impressive, and very solid looking oak door, at which he knocked tentatively. He didn't like dealing with wizards.

"Hang on a moment!" called a voice from inside.

There was a small noise, like a firework exploding.

"Damn" said the same voice, and coughed. "I told you we shouldn't have tried to explode Stutthammer's Theory at the same time as Doubtscrew's Proposal of Thaumic Uncertainty."

There was a pause.

"That wasn't Doubtscrew's Proposal" said another voice.

Another pause.

"Really? What the hell was it, then?"

"I don't know, I thought you were looking after that!"

"No, I was taking a reading from Hex: I thought you were looking after Doubtscrew!"

"Well...at least we know that Strutthammer doesn't calculate. The slood ratings were much higher than he had originally stated, and the blit rating... off the scale."

Vimes cleared his throat.

"Oh, sorry." The door opened, and a young man with glasses looked out. "Hello. I think you've got the wrong door..."

"Mr. Stibbons?"

"Er, yes, that's me." He looked at Vimes nervously, noticing the Watch badge. "Have I done something wrong?"

"I wish to make enquiries about a stolen book of magic."

"You'd better come in." The wizard showed Vimes in. "Most of the smoke's cleared now: I don't think it's dangerous."

Typical wizard, thought Vimes. Do things first, wonder if they're dangerous afterwards.

Mr. Stibbons cleared a chair of papers covered in neat, rounded writing and nervously ushered Vimes towards it.

"Please sit down. Now, how can I help you? Don't mind the mess, it's only slood. Nothing to worry about."

"A book called the Octavo Explained has gone missing. I understand from the Arch-chancellor that you may be able to find it. With a...thaumometer?"

"Ah. I'm afraid it doesn't quite work like that. You would have to go to every house in the city and hold it outside the door to find out if they had it. I may be able to determine which part of the city it is in, though, If that would help."

Vimes nodded. He noticed the second person he had heard through the door standing in front of a very peculiar...machine. There was a large glass sphere, that was certain, and many, many pipes coming from it, some of which seemed to pass through each other and go back to exactly the same place they came from, serving no apparent purpose. Mr. Stibbons saw him looking.

"That's Hex. Our thinking machine. I'm going to link the thaumometer to Hex, and then ask him to search for an unfamiliar magical presence" he explained.

"You can do that?" asked Vimes incredulously.

"Oh yes. Hex can cover a much wider area than the thaumometer on its own. Wonderful thing. Alex, just connect this to the input socket, will you? I'll program him: I think I've worked out how he works with the thaumometer now" ordered Stibbons. "Commander Vimes, can I offer you a drink?"

"No, thank you. I'd just like to know where this damned book is. I have a horrible feeling about it."

"I'm not surprised. It is called the Octavo Explained."

"Is that bad?"

"Very. You know Professor Rincewind? He looked in the Octavo once, and he's never been able to learn any spell other than the Octavo spell that lodged itself into his brain. At least, that's his excuse." Stibbons sniffed. "Have you got that ready, Alex?"

"Yes, I think so." His assistant turned around. "Is it supposed to be glowing blue?"

"I think so. What kind of blue?" queried Stibbons.

"Turquoise, I think, possibly with a hint of duck-egg" answered Alex.

"Oh gods, what have you done now?"

Vimes rubbed his face wearily as Ponder Stibbons hurried over to the thinking machine. This was going to be a long day.