A  NEW YORK TIMES BESTSELLER Steam is rising over Discworld, driven by Mister Simnel, the man with a flat cap and a sliding rule. He has produced a great clanging monster of a machine that harnesses the power of all of the elements--earth, air, fire, and water--and it's soon drawing astonished crowds.      To the consternation of Ankh-Morpork's formidable Patrician, Lord Vetinari, no one is in charge of this new invention. This needs to be rectified, and who better than the man he has already appointed master of the Post Office, the Mint, and the Royal Bank: Moist von Lipwig. Moist is not a man who enjoys hard work--unless it is dependent on words, which are not very heavy and don't always need greasing. He does enjoy being alive, however, which makes a new job offer from Vetinari hard to refuse.      Moist will have to grapple with gallons of grease, goblins, a fat controller with a history of throwing employees down the stairs, and some very angry dwarfs if he's going to stop it all from going off the rails . . .