Iron seeks out other iron. Things spin. In the absence of any gods to do the creating of life, life has managed, against the odds, to create itself. Yet the humans who have evolved on the planet believe in their hearts that there are such things as gods, magic, cosmic purpose and million-to-one chances that crop up nine times out of ten. They seek stories in the world which the world, regrettably, is not equipped to tell.

The wizards, feeling somewhat guilty about this, have intervened several times in the history of Roundworld when it seemed to them to be on the wrong track. They encouraged fish (or fish-like creatures) to leave the seas, they visited the proto-civilisations of dinosaur-descendants and crabs, they despaired at the way ice and falling comets wiped out higher life forms so often - and they found some monkeys who were obsessed with sex and were quick learners, especially if sex was involved or could, by considerable ingenuity, be made to be involved.

Again the wizards intervened, teaching them that fire was not for having sex with and in general encouraging them to get off the planet before the next big extinction.

In this they have all been guided by Hex, UU's magical thinking engine, which is immensely powerful in any case, and with Roundworld, which from Hex's point of view is a mere sub-routine of Discworld and is practically godlike, although more patient.

The wizards think 'they have sorted it all out. The monkeys have learned about their permanently threatened world via a type of technomancy called Science and may yet escape frozen doom.

And yet...

The thing about best laid plans is that they don't often go wrong. They sometimes go wrong, but not often, because of having been, as aforesaid, the best laid. The kind of plans laid by wizards, who barge in, shout a lot, try to sort it all out by lunchtime and hope for the best, on the other hand ... well, they go wrong almost instantly.