The acclaimed Science of Discworld centred on an original Pratchett story about the Wizards of Discworld. In it they accidentally witnessed the creation and evolution of our universe, a plot which was interleaved with a Cohen & Stewart non-fiction narrative about Big Science. In The Science of Discworld II our authors join forces again to see just what happens when the wizards meddle with history in a battle against the elves for the future of humanity on Earth. London is replaced by a dozy Neanderthal village.

Roundworld is in trouble again, and this time it looks fatal. Having created it in the first place, the wizards of Unseen University feel vaguely responsible for its safety. They know the creatures who lived there escaped the impending Big Freeze by inventing the space elevator - they even intervened to rid the planet of a plague of elves, who attempted to divert humanity onto a different time track. But now it's all gone wrong - Victorian England has stagnated and the pace of progress would embarrass a limping snail.

The fourth book in the Science of Discworld series, and this time around dealing with the really big questions, Terry Pratchett’s brilliant new Discworld story Judgement Day is annotated with very big footnotes (the interleaving chapters) by mathematician Ian Stewart and biologist Jack Cohen, to bring you a mind-mangling combination of fiction, cutting-edge science and philosophy.Marjorie Daw is a librarian, and takes her job – and indeed the truth of words – very seriously. She doesn’t know it, but her world and ours – Roundworld – is in big trouble.

To the consternation of the patrician, Lord Vetinari, a new invention has arrived in Ankh-Morpork - a great clanging monster of a machine that harnesses the power of all of the elements: earth, air, fire and water. This being Ankh-Morpork, it’s soon drawing astonished crowds, some of whom caught the zeitgeist early and arrive armed with notepads and very sensible rainwear.

Time is a resource. Everyone knows it has to be managed. And on the Discworld that is the job of the Monks of History, who store it and pump it from the places where it's wasted (like the underwater; how much time does a codfish need?) to places like cities, where there's never enough time. But the construction of the world's first truly accurate clock starts a race against, well, time for Lu Tze and his apprentice Lobsang Ludd.

Sam Vines is a man on the run. Yesterday, he was a duke, a chief of police, and an ambassador. Now he has nothing but his native wit and the gloomy trousers of Uncle Vanya. And if he can't make it through the forest to civilisation, there's going to be a terrible war. But there are monsters on his trail. They're werewolves - and they're catching up. Sam Vimes is out of time and already out of breath....

Roundworld is in trouble again, and this time it looks fatal. Having created it in the first place, the wizards of Unseen University feel vaguely responsible for its safety. They know the creatures that lived there escaped the impending Big Freeze by inventing the space elevator - they even intervened to rid the planet of a plague of elves, who attempted to divert humanity onto a different time track. But now it's all gone wrong - Victorian England has stagnated, and the pace of progress would embarrass a limping snail.

It begun as a sudden strange fancy...Polly Perks had to become a boy in a hurry. Cutting off her hair and wearing trousers was easy. Learning to fart and belch in public and walk like an ape took more time. And now she's enlisted in the army and searching for her lost brother. But there's a war on. There's always a war on. And Polly and her fellow recruits are suddenly in the thick of it, without any training, and the enemy is hunting them.

Three witches gathered on a lonely heath. A king cruelly murdered, his throne usurped by his ambitious cousin. A child heir and the royal crown, both missing.

If you find yourself ruminating on questions like "Where have all the dragons gone?" then this is the story for you. Explore the crazy, creepy land called Discworld, where you'll discover that the dragons aren't asleep or dead - they're dormant, packed in like huge, scaly sardines. Join in the search for the key to their closed-in, comatose world in this eighth fantastical Discworld novel.

The town of Ankh-Morpork is in big trouble and the City Watch is desperate for a few good men to protect it. But all they've got are the dwarves Corporal Carrot and Lance-constable Cuddy, the troll Lance-constable Detritus, Lance-constable Angua, who is believed to be a woman and, worst of all, Corporal Nobbs, who has been disqualified from the human race for shoving! These underdogs need all the help they can get, for they've been given only 24 hours to clean up the war-torn town.

It's an offer you can't refuse. Who would not wish to be the man in charge of Ankh-Morpork's Royal Mint and the bank next door? It's a job for life. But, as former con-man Moist von Lipwig is learning, the life is not necessarily for long. The Chief Cashier is almost certainly a vampire. There's something nameless in the cellar (and the cellar itself is pretty nameless), and it turns out that the Royal Mintruns at a loss.

Who's murdering harmless old men? Who's poisoning the Patrician? As autumn fogs hold Ankh-Morpork in their grip, the City Watch has to track down a murderer who can't be seen. Maybe the golems know something - but the solemn men of clay, who work all day and night and are never any trouble to anyone, have started to commit suicide....

Eleven-year-old Tiffany Aching wants to be a real witch. But a real witch doesn't casually step out of her body, leaving it empty. Tiffany does, and there's something just waiting for a handy body to take over. Something ancient and horrible, which can't die.

Finding himself alone on a desert island when everything and everyone he knows and loved has been washed away in a huge storm, Mau is the last surviving member of his nation. He's also completely alone - or so he thinks until he finds the ghost girl. She has no toes, wears strange lacy trousers like the grandfather bird and gives him a stick which can make fire. Daphne, sole survivor of the wreck of the Sweet Judy, almost immediately regrets trying to shoot the native boy.