'The context does not, I feel, suggest the Dean,' he said.

'Er... what context would this be?' said Ridcully.

The Patrician picked up his walking stick.

'Come this way,' he said. 'I suppose you had better see for yourself. It is very vexing.'

Ridcully looked around with interest as he followed Lord Vetinari. He did not often have a chance to see the gardens, which had been written up in the 'How Not To Do It' section of gardening manuals everywhere.

They had been laid out, and a truer phrase was never used, by the renowned or at least notorious landscape gardener and all round inventor 'Bloody Stupid' Johnson, whose absent-mindedness and blindness to elementary mathematics made every step a walk with danger. His genius... well, as far as Ridcully understood it, his genius was exactly the opposite of whatever kind of genius it was that built earthworks that tapped the secret yet beneficent forces of the leylines.

No-one was quite certain what forces Bloody Stupid's designs tapped, but the chiming sundial frequently exploded, the crazy paving had committed suicide and the cast iron garden furniture was known so have melted on three occasions.

The Patrician led the way through a gate and into something like a dovecot. A creaking wooden stairway led around the inside. A few of Ankh-Morpork's indestructible feral pigeons muttered and sniggered in the shadows.

'What's this?' said Ridcully, as the stairs groaned under him.

The Patrician took a key out of his pocket. 'I have always understood that Mr Johnson originally planned this to be a beehive,' he said. 'However, in the absence of bees ten feet long we have found... other uses.'

He unlocked a door to a wide, square room with a big unglazed window in each wall. Each rectangle was surrounded by a wooden arrangement to which was affixed a bell on a spring. It was apparent that anything large enough, entering by one of the windows, would cause the bell to ring.