There was a muted thump from under their feet and the faint, happy sound of Schleppel.

"Oh, wow! Rats, too!"

"I went up and tried to tell you wizards," said Mrs. Cake, primly. "An' no-one listened. I knew they weren't going to, but I ‘ad to try, otherwise I wouldn't ‘ave known."

"Who did you speak to?"

"The big one with the red dress and a moustache like he's trying to swallow a cat."

"Ah. The Archchancellor, " said Windle, positively.

"And there was a huge fat one. Walks like a duck."

"He does, doesn't he? That was the Dean," said Windle.

"They called me their good woman, " said Mrs. Cake. "They told me to be about my business. Don't see why I should go around helpin' wizards who call me a good woman when I was only trying to help."

"I'm afraid wizards don't often listen," said Windle. "I never listened for one hundred and thirty years."

"Why not?"

"In case I heard what rubbish I was saying, I expect. What's happening, Mrs. Cake? You can tell me. I may be a wizard, but I'm a dead one. Schleppel told me it was all due to life force."

"It's buildin' up, see?"

"What does that mean?"

"There's more'f it than there should be. You get" - she waved her hands vaguely – "when things are like in a scales only not the same on both sides..."

"Imbalance?"

Mrs. Cake, who looked as though she was reading a distant script, nodded.

"One of them things, yeah... see, sometimes it just happens a little bit, and you get ghosts, because the life is not in the body any more but it hasn't gone... and you get less of it in the winter, because it sort of drains away, and it comes back in the spring... and some things concentrate it..."

Modo the University gardener hummed a little tune as he wheeled the strange trolley into his private little area between the Library and the High Energy Magic building, with a load of weeds bound for composthood.

There seemed to be a lot of excitement around at the moment. It was certainly interesting, working with all these wizards.

Teamwork, that's what it was. They looked after the cosmic balance, the universal harmonies and the dimensional equilibriums, and he saw to it that the aphids stayed off the roses.

There was a metallic tinkle. He peered over the top of the heap of weeds.

"Another one?"

A gleaming metal wire basket on little wheels sat on the path.

Maybe the wizards had bought it for him? The first one was quite useful, although it was a little bit hard to steer; the little wheels seemed to want to go in different directions. There was probably a knack.

Well, this one would be handy for carrying seed trays in. He pushed the second trolley aside and heard, behind him, a sound which, if it had to be written down, and if he could write, he would probably have written down as: glop.

He turned around, saw the biggest of the compost heaps pulsating in the dark, and said, "Look what I brought you for your tea!"

And then he saw that it was moving.

"Some places, too... " said Mrs. Cake.

"But why should it build up?" said Windle.

"It's like a thunderstorm, see? You know how you get that prickly feelin' before a storm? That's what's happening now."

"Yes, but why, Mrs. Cake?"

"Well... One-Man-Bucket says nothing's dying."

"What?"

"Daft, isn't it? He says lots of lives are ending, but not going away. They're just staying here."

"What, like ghosts?"

"Not just ghosts. Just - it's like puddles. When you get a lot of puddles, it's like the sea. Anyway, you only get ghosts from things like people. You don't get ghosts of cabbages."

Windle Poons sat back in his chair. He had a vision of a vast pool of life, a lake being fed by a million short-lived tributaries as living things came to the end of their span. And life force was leaking out as the pressure built up. Leaking out wherever it could.

"Do you think I could have a word with One –" he began, and then stopped.

He got up and lurched over to Mrs. Cake's mantel-piece.

"How long have you had this, Mrs. Cake?" he demanded, picking up a familiar glassy object.

"That? Bought it yesterday. Pretty, ain't it?"

Windle shook the globe. It was almost identical to the ones under his floorboards. Snowflakes whirled up and settled on an exquisite model of Unseen University.

It reminded him strongly of something. Well, the building obviously reminded him of the University, but the shape of the whole thing, there was a hint of, it made him think of...

... breakfast?

"Why is it happening?" he said, half to himself. "These damn things are turning up everywhere."

The wizards ran down the corridor.

"How can you kill ghosts?"

"How should I know? The question doesn't usually arise!"

"You exorcise them, I think."

"What? Jumpin' up and down, runnin' on the spot, that kind of thing?"

The Dean had been ready for this. "It's spelled with an "O", Archchancellor. I don't think one is expected to subject them to, er, physical exertion."

"Should think not, man. We don't want a lot of healthy ghosts buzzin' around."

There was a blood-curdling scream. It echoed around the dark pillars and arches, and was suddenly cut off.

The Archchancellor stopped abruptly. The wizards cannoned into him.

"Sounded like a blood-curdlin' scream," he said. "Follow me!"

He ran around the corner.

There was a metallic crash, and a lot of swearing.

Something small and striped red and yellow, with tiny dripping fangs and three pairs of wings, flew around the corner and shot over the Dean's head making a noise like a miniature buzzsaw.

"Anyone know what that was?" said the Bursar, faintly. The thing orbited the wizards and then disappeared into the darkness of the roof. "And I wish he wouldn't swear so."

"Come on," said the Dean. ‘We'd better see what's happened to him."

"Must we?" said the Senior Wrangler.

They peered around the corner. The Archchancellor was sitting up, rubbing his ankle.

"What idiot left this here?" he said.

"Left what?" said the Dean.

"This blasted wire baskety wheely thing," said the Archchancellor. Beside him, a tiny purple spider-like creature materialised out of the air and scuttled towards a crevice. The wizards didn't notice it.

"What wire baskety wheely thing?" said the wizards, in unison.

Ridcully looked around him.

"I could have sworn –" he began.

There was another scream.

Ridcully scrambled to his feet.

"Come on, you fellows!" he said, limping heroically onwards.

"Why does everyone run towards a blood-curdling scream?" mumbled the Senior Wrangler. "It's contrary to all sense."

They trotted out through the cloisters and into the quadrangle.

A rounded, dark shape was squatting in the middle of the ancient lawn. Steam was coming out of it in little, noisome wisps.

"What is it?"

"It can't be a compost heap in the middle of the lawn, can it?"

"Modo will be very upset."

The Dean peered closer. "Er... especially because, I do believe, that's his feet poking out from under it..."

The heap swivelled towards the wizards and made a glop, glop noise.

Then it moved.

"Right, then," said Ridcully, rubbing his hands together hopefully, "which of you fellows has got a spell about them at the moment?"

The wizards patted their pockets in an embarrassed fashion.

"Then I shall attract its attention while the Bursar and the Dean try to pull Modo out," said Ridcully.

"Oh, good, " said the Dean faintly.

"How can you attract a compost heap's attention?" said the Senior Wrangler. "I shouldn't think it's even got one."

Ridcully removed his hat and stepped gingerly forward.