The oldest and most inscrutable empire on the Discworld is in turmoil, brought on by the revolutionary treatise What I did on My Holidays. Workers are uniting, with nothing to lose but their water buffaloes. War (and Clancy) are spreading through the ancient cities.

And all that stands in the way of terrible doom for everyone is:

Rincewind the Wizard, who can't even spell the word 'wizard'...

Cohen the barbarian hero, five feet tall in his surgical sandals, who has had a lifetime's experience of not dying...

and a very special butterfly.