'DON'T PUT YOUR TRUST IN REVOLUTIONS. THEY ALWAYS COME ROUND AGAIN. THAT'S WHY THEY'RE CALLED REVOLUTIONS. PEOPLE DIE, AND NOTHING CHANGES.'

The twenty-fifth of May is an important, sombre day in Ankh-Morpork - the anniversary of one of the city's bloodiest rebellions.

But crime stops for nothing, as Commander Sam Vimes of the City Watch knows. When a notorious serial killer emerges from hiding, the chase leads the Watch to the roofs of Unseen University where a magical storm ...