O idealista anano de case dous metros, Cenoria, entra na Garda da Noite da cidade de Ankh-Morpork, a máis grandiosa do Mundodisco, para arrestar ladróns asasinos coa Lei na man, algo nunca antes visto. Os tres veteranos que integran esta garda escangallada e sen sentido son o capitán Vimes, o sarxento Colon e o cabo Nobbs.
Xuntos terán que lidar cunha rutina que rompe pois, malia que se creu extinto durante moito tempo, un magnífico exemplar de draco nobilis («dragón nobre», para quen non entenda a cursiva) apareceu na cidade. Este perigoso visitante non só ten o desagradábel costume de calcinar todo ao seu paso, senón que, en pouco tempo, é coroado Rei (á fin e ao cabo, é un dragón nobre…). Como chegou alí? Poderá a Garda da Noite restaurar a orde dunha cidade sen lei? Maxia, caos e un dragón asexador… Quen podería pedir máis?
Sir Terence David John Pratchett was an English author, humorist, and satirist, best known for the Discworld series of 41 comic fantasy novels published between 1983–2015, and for the apocalyptic comedy novel Good Omens (1990), which he co-wrote with Neil Gaiman. Pratchett's first novel, The Carpet People, was published in 1971. The first Discworld novel, The Colour of Magic, was published in 1983, after which Pratchett wrote an average of two books a year. The final Discworld novel, The Shepherd's Crown, was published in August 2015, five months after his death. With more than 100 million books sold worldwide in 43 languages, Pratchett was the UK's best-selling author of the 1990s. He was appointed an Officer of the Order of the British Empire (OBE) in 1998 and was knighted for services to literature in the 2009 New Year Honours. In 2001 he won the annual Carnegie Medal for The Amazing Maurice and His Educated Rodents, the first Discworld book marketed for children. He received the World Fantasy Award for Life Achievement in 2010. In December 2007 Pratchett announced that he had been diagnosed with early-onset Alzheimer's disease. He later made a substantial public donation to the Alzheimer's Research Trust (now Alzheimer's Research UK, ARUK), filmed three television programmes chronicling his experiences with the condition for the BBC, and became a patron of ARUK. Pratchett died on 12 March 2015, at the age of 66.