Terry Pratchett's Raising Steam is the 40th (!) novel in the Discworld series. It's just come out in the UK (the US edition comes out in March) and it's a tremendous synthesis of everything that makes Pratchett one of the world's most delightful writers. It's a curious thing: a fantasy novel about modernity and reactionaries, a synthesis of technological optimism and a curious sort of romantic mysticism.

Raising Steam follows on from 2007's Making Money, and features the delightful Moist von Lipwig, as well as the characters who often accompany him, such as Lord Vetinari, William de Worde, Adora Belle Dearheart, and, notably, Harry King. It's the story of an inventor, Dick Simnel, who masters steam, invents the railroad, and comes to Ankh-Morpork to make it a reality. Working against Simnel and his "railroading time" is a faction of reactionary dwarfs, deep-down grags who hate modernity and the mixing of dwarfs with the Discworld's other species. The grags inspire a wave of terrorist violence, starting with attacks on the clacks towers and moving onto the railroad itself.

Longstanding Pratchett fans know that the series started off with a light (even slight), silly tone — one that deepened, book by book, into something altogether more serious. Raising Steam has a lot more of the feel of that early Pratchett, with some very silly wordplay (the Marquis of Aix en Pains!) and a serious quantity of funny/silly footnotes. Even the dwarfish names tilt more towards Snow White jokes than references to Icelandic lore. But as the synopsis above implies, this is also one of the darkest of the Pratchett novels, a thoughtful and often graphically violent story about modernity, terrorism, and technology's discontents.

Longrunning fantasy series have a (deserved) reputation for tedium and repetition, but that's not the case with Pratchett. The Discworld story has steadily moved towards this point, through a narrative that suggests that, at every turn, the march of technology is a force for liberation and human dignity. Raising Steam is, among other things, a novel about universal suffrage, driven by technological change. As communications and transport technology bring the Discworld's distant regions ever closer, the personhood of every species, from golems to goblins, and every gender, is presented as an inevitable consequence.

Pratchett's dallied with the theme of technology as a force superior to mysticism and magic before (see, for example, Pyramids), but never with such a keen enthusiasm. Paradoxically, Pratchett gives technology a kind of mystical spirit — his railroad is a kind of living god (a kind of positive version of the "gonne" in Men at Arms or the films in Moving Pictures) that ensnares the imaginations of the people who behold it, driving them to spread it far and wide. And unlike the previous anthropomorphized technologies of Discworld, the railroad is a great liberator, a greater magic than that of the wizards.

Most of the Discworld novels stand alone, but not this one. From the intertextual references (Dick Simnel is the son of Ned Simnel, a minor but crucial character in Reaper Man) to the complex relationship between Commander Vimes and the dwarfs (not to mention the military mystery of Koom Valley, presented in Thud), this is a book that practically requires you to have read all 39 of the previous volumes before you can get to grips with it.

But it's worth it. This is a surprisingly layered and sneaky sort of book. Pratchett's trick of presenting technophilia as a kind of magic is not to be missed. And this is a long book, with an oddly paced second act that includes a literal whistle-stop tour of many new places on the Discworld, places that Pratchett clearly has vividly imagined but where he's never taken us before. Many of these are, strictly speaking, unnecessary to the story, but on second reading, they give a sense of the world's vastness and a sharp contrast to the collapse of distance created by technological shifts.

Pratchett's health is poor (he has rare, early onset Alzheimer's), and according to the author's note, he dictated this book to his computer with text-to-speech software. It retains an unmistably Pratchettesque voice, but there's something altogether new here — an oddly purer form. He's never quite balanced whimsy and gravitas as carefully as this, and it works beautifully. This is a spectacular novel, and a gift from a beloved writer to his millions of fans.

Raising Steam [UK]

Raising Steam [US, pre-order]