The Bursar had calmed down considerably. He was now walking forwards and had regained control of his eyes but was still prone to the odd bout of rhyming. Harry and Ron had explained to Ponder about what had happened in Snape's class. Ponder had summoned a couple of the university Bledlows to take the body of Professor Eugene Short to a more private room till the necessary arrangements could be made.

"It's uncanny really; the two of them could be brothers" said The Bursar, making Ron jump. That was the first sane thing he had said all day.

"But Harry doesn't have any brothers" he managed. The Bursar nodded

"In your world perhaps, but not in others. Oh dear" Ron watched as The Bursar produced a small pill box from one of the many pockets of his robe. The box read 'Dried Frog Pills'.

"Ha-ha! Found it!" a cry came from the depths of the shelves. The wizards followed the sound to its source. There is any number of ways to describe what The Dean had discovered. For the sake of narrative I shall use the one that the Chair of Indefinite studies gave. It looked like a purple swirly thing with octarine in the middle.

"Gods, Ponder was right, there is a portal" said the Senior Wrangler. Ridcully picked up a stray volume and threw it into the depths before anybody could stop him. It span slowly in the octarine core before it disappeared. A second later, accompanied by thick smoke, a hat appeared. It was probably one red, and hastily re-embroidered where the sequins had fallen off was the word 'WIZZARD'.

"That's Rincewind's hat!" The Dean yelled

"You mean that there are people from here in Hogwarts?" said Harry

"I think he's right, it looks like when the portal pulls something into it from one side it has to pull something else through from the other to keep itself in balance" said Ponder.

"If the Ponders are right then there will be three things from here on the other side. Rincewind, obviously, and his Luggage will probably be big enough to count as a person. Who else?" Ridcully mused.

"My name is Harry" said Harry

"Harry Ponder?"

"Harry Potter!"

"Close enough" Ridcully decided. Harry went to argue some more but Ponder stopped him and shook his head. Ron went over to his friend.

"These people are mental! Harry, have you noticed how all the books keep trying to take off?" Ron asked him.

"The Librarian knows how to calm them down" said the Lecturer in Recent Runes, oblivious to the fact that he had just been called mental, "Where is The Librarian anyway?"

Everyone looked at the portal

-

On the other side of the portal Rincewind was wondering the exact same thing. He wasn't a happy wizard. Snape's idea of helping him down had been to zap him with his wand until he had let go. The portal was in the middle of Snape's dungeon, so that explained his foul mood at least. Unless, Rincewind shuddered, he was like that all the time. Dumbledore and McGonagall were inspecting the portal when Rincewind and Snape arrived. They were just in time for a book to be spat out of the centre. It smacked Rincewind in the head and knocked his hat off. A moment later and it was sucked into the vortex.

"Hey! My hat!"

"How tragic" Snape commented drolly

"Interesting, it draws matter into itself to keep in balance with whatever comes through" Dumbledore said

"And that's where you think Potter and Weasley are?" asked Professor McGonagall.

"Undoubtedly. And now to see how they are" Dumbledore drew his wand and drew a lazy circle in the air, leaving a fine golden trail behind. The circle solidified and transformed itself into two thin mirrors that fit together to form a circle. He handed one half to Professor McGonagall and stepped up to the portal.

"I sincerely hope that whoever threw the book doesn't have butterfingers" he said before he let it go. The mirror spun in the centre before vanishing and being replaced by a small pillbox that was locked in a ballistic trajectory aimed squarely at Rincewind's face. Snape caught it. For one horrible moment the Potions Master looked oddly familiar to Rincewind, who tried to put the thought out of his head. Dumbledore muttered a spell and tapped the mirror.

"Hello there fellows, my name is Albus Dumbledore, Headmaster at Hogwarts school of Witchcraft and Wizardry. I believe that there has been something of a mishap" he spoke into the mirror. A moment later and a familiar voice answered

"Mustrum Ridcully, Archchancellor of Unseen University, at your service. We appear to have some of your students here" Dumbledore smiled.

"And we appear to be host to one of your wizards and your Librarian"

"Oh dear, well we're going to need him back. The books have gotten used to him, I don't think there's another soul on the whole Disc brave enough to train up for his post"

"Well, we'd best see what can be done. How many people came through at your end?" McGonagall looked a little confused, the man had said 'the whole disc'. What did that mean?

"Well, err, three, but ones dead. The older one, the boys are quite alright"

"Ahh, well that presents a problem. You see, as I understand it there needs to be an equal amount of exchange on each side" said Dumbledore. There was the sound of muted muttering as this was explained in terms that the wizards of Unseen University understood. The muttering grew into bickering. Finally, over the noise, there was an answer.

"Excuse me sir, but from what I can see the portal pulls objects through at random to correct the imbalance that occurs by sending something through. At the moment there's no guarantee that we can safely switch people from one dimension to the other in any predictable manner. There's already been one death because of this and I don't think that we should rush into things without understanding what we are dealing with a little better"

"An excellent point, Mr…"

"Ponder Stibbons, sir"

"Yes. You bear quite a resemblance to young Harry" Dumbledore observed. "Anyway, we are agreed that while we don't know what will happen if we try sending people through portals, there are all perfectly safe where they are until we can eliminate as much risk as possible"

"Yes sir, I think that would be for the best" Ponder agreed. In the background a voice that Rincewind recognised as The Dean was saying that "Rincewind is a skinny chap, isn't he? Why not just send through some old rubbish for him? He can't weigh that much"

"Dean! We are not sending any rubbish through any portals! Or have you forgotten what happened last time?"

"That was different. For a start it wasn't a portal to another… wossname…"

"Dimension?"

"That's the one"

Dumbledore smiled and nodded into the mirror, and then he put it down on Snape's desk.

"Well, I think that settles it. Professor Rincewind, the students have been excused from Defence against Dark arts classes for the rest of the day, and there is a Hogsmeade trip planned for tomorrow so you will have plenty of time to prepare. I also feel that you may want to get yourself some provisions, a new hat and so forth. As I understand it several house elves have tried to unpack your Luggage and have disappeared, as it were" Rincewind didn't answer. By the looks of things he was definitely trying to faint again but the potion he had been given was still in effect

"Err… I just… go… go… and prepare… just go and… and…" he babbled as he backed towards the door. He reached the door. He ran. Snape made a disgusted sound and left the room. That left Dumbledore and McGonagall.

"Professor, you knew. Didn't you?" She asked.

"Knew what Minerva?" said Dumbledore with a smile

"About Harry and Ron. You offered Rincewind the job before you contacted his universe"

"Harry and Ron are safe there, in the last place anyone could possibly imagine looking for them. Now, I was thinking that someone should accompany Rincewind tomorrow. Miss Grainger possibly?"

Professor McGonagall nodded.

"I see" She said.

-

The wizards were still arguing.

"And then we found that the other side came out in the attic! Can you imagine it?" said the Chair of Indefinite Studies. Chair was the right name for him, Harry reflected, it was the way the man dressed and the fact that he was roughly chair shaped. Harry felt a barely suppressed urge to rummage for loose change every time he looked at the man.

"What are they talking about" Ron asked The Bursar

"An incident years ago concerning Archchancellor Weatherwax." He explained the finer details quietly. Ron looked incredulous.

"Are you sure you've had enough of those pills?" he asked.

The wizards continued to ague among themselves. Mainly over what would happen without the Librarian. Harry, Ron, Ponder and The Bursar withdrew to a safe distance.

"So, if this is a different universe, how come you and me look so much alike?" Harry asked Ponder, who had been wondering this too.

"I've been thinking about this and I have a theory. What I think is that there is only a limited amount of ways that matter in a universe can arrange itself. While the number may be extremely high there are still times when one pattern can look so similar to another that it can be hard to tell the difference"

"Harry, this is creepy, he's like you with Hermione's brain!" said Ron

"I'm sure that it is very interesting, but I'm afraid I'm going to have to interrupt your discussion" said a voice from the door. Every wizard turned slowly to face the tall thin figure dressed in black.

"Now, would one of you gentlemen mind explaining to me why you are blowing holes in my city? I was under the impression that that was the Alchemists job" said the Patrician of Ankh-Morpork, Lord Havelock Vetinari.