This is book number 22 in the Discworld series.
There's big trouble at the Unseen University, Ankh-Morpork's lone institute of higher learning. A professor is missing—and the one person who can find him is not only the most inept magician the school ever produced, but currently stranded on the unfinished down-under continent of Fourecks.
As the UU faculty tries to bring him back, Rincewind is having troubles of his own, thanks to a pushy mystical kangaroo trickster named Scrappy and a mob of Fourecks hooligans who are out to hang him. All his problems would be solved if he could just make it rain . . . for the first time ever. And if the time-traveling professors can get to the right millennium . . .
Sir Terry Pratchett was the internationally bestselling author of more than thirty books, including his phenomenally successful Discworld series. His young adult novel, The Amazing Maurice and His Educated Rodents, won the Carnegie Medal, and Where's My Cow?, his Discworld book for “readers of all ages,” was a New York Times bestseller. His novels have sold more than seventy five million (give or take a few million) copies worldwide. Named an Officer of the British Empire “for services to literature,” Pratchett lived in England. He died in 2015 at the age of sixty-six.