Guards! Guards! is the eighth Discworld novel by Terry Pratchett, first published in 1989. It is the first novel about the Ankh-Morpork City Watch. The first Discworld computer game borrowed heavily from Guards! Guards! in terms of plot.
The story follows a plot by a secret brotherhood, the Unique and Supreme Lodge of the Elucidated Brethren of the Ebon Night, to overthrow the Patrician of Ankh-Morpork and install a puppet king, under the control of the Supreme Grand Master. Using a stolen magic book, they summon a dragon to strike fear into the people of Ankh-Morpork.
Once a suitable state of terror and panic has been created, the Supreme Grand Master proposes to put forth an "heir" to the throne, who will slay the dragon and rid the city of tyranny.