Terry Pratchett’s. Guards Guards (Full AudioBook)

A secret monastic order plots to overthrow the Patrician of Ankh-Morpork and install a puppet monarch under the control of the Order. They summon a dragon to terrorise the city and plan to have the puppet "slay" the dragon and claim to be the lost heir of the defunct royal house.

The Night Watch is generally seen as both corrupt and incompetent, starts to change with the arrival of idealistic new recruit Carrot Ironfoundersson, a human orphan raised by dwarfish parents. When the Librarian of the Unseen University (an orangutan) reports a book of magic stolen, Vimes links the theft to the dragon's appearances. The Watch's investigation makes the acquaintance of Lady Sybil Ramkin, who breeds small swamp dragons, and gives an underdeveloped dragon named Errol to the Watch as a mascot.