Guards! Guards!

The eighth novel in Terry Pratchett's comic fantasy Discworld series, and the first to feature the City Watch, is set in Ankh-Morpork, the largest city on the Disc, a flat world resting on four elephants atop a giant turtle. Lord Vetinari, the Patrician, rules by ensuring competing factions of merchants, thieves, assassins, and wizards remain too busy undercutting one another to threaten him. He legalized the Thieves' Guild years ago, making organized crime responsible for keeping theft within agreed limits, an arrangement that rendered the city's police force, the Night Watch, nearly obsolete.

Captain Sam Vimes commands what remains of the Watch: himself, the timid Sergeant Colon, and Corporal Nobbs, a small, disreputable man. Vimes has a severe alcohol addiction and collapses nightly in the gutter outside the Watch House, nursing a bleak love for a city that has no use for him. The Watch's duties have shrunk to walking the streets, ringing a bell, and shouting that all is well.

Into this decayed institution arrives Carrot Ironfoundersson, a young man of enormous build raised by dwarfs in a mountain gold mine. His adoptive father revealed Carrot is human, found as a toddler near burned carts, and sent him to Ankh-Morpork to join the Watch. Carrot carries a plain, non-magical sword recovered from the wreckage and a copy of The Laws and Ordinances of the Cities of Ankh and Morpork, which he has memorized and intends to enforce literally. Within hours, he arrests the head of the Thieves' Guild and defeats every patron of a tavern in a brawl. The Patrician's secretary, Lupine Wonse, summons Vimes and orders him to bring the newcomer under control.

Meanwhile, a secret society called the Elucidated Brethren of the Ebon Night meets in the city's back streets, led by the Supreme Grand Master. He exploits the members' resentments, suggesting that a royal heir to Ankh-Morpork's defunct monarchy might still exist. Using The Summoning of Dragons, a book stolen from the Library at Unseen University, the city's school of wizardry, the Supreme Grand Master teaches the Brethren to summon a dragon from the dimension where the great dragons dwell. The plan: summon the dragon to terrorize the city, then produce a young man who will "slay" it with a jeweled sword while the Brethren stop summoning, causing the creature to vanish. The grateful populace will crown the young man king while the Supreme Grand Master rules from behind the throne.

The summonings begin. A thief is incinerated in the Shades. The Watch finds huge talon prints emerging from an alley that nothing ever entered. Vimes secretly casts a footprint in plaster and takes it to Lady Sybil Ramkin, a wealthy aristocrat who breeds small swamp dragons, creatures so biologically unstable they frequently explode. She identifies the print as belonging to Draco nobilis, the Noble dragon, a species thought extinct, and theorizes that the creatures retreated to a dimension where magic sustained their impossible biology. A misfit dragon in her kennels catches Vimes's eye. Lady Ramkin gives the malformed creature to the Watch; they rename him Errol.

The great dragon appears over the city, setting precise fires with suspicious accuracy and destroying the Watch House. Vimes survives when Carrot grabs him and leaps from the roof. The Supreme Grand Master's plan reaches its climax: In the Plaza of Broken Moons, his cousin faces the dragon. The Supreme Grand Master blocks the dragon's flame with his will, the young man strikes, and the dragon vanishes in purple smoke, leaving no remains. The crowd carries the hero to the palace, Vetinari is locked in his own dungeons, and the city crowns a king. Vimes, alone in the Watch House, writes out his suspicions: no remains, a conveniently timed king, a dragon that could not flame at the crucial moment.

The dragon, however, has its own plans. Furious at being summoned and dismissed, it draws on the vast magical energy stored in the University Library, as lightning arcs between the plaza and the Library to pull the creature back into the world. Now self-sustaining, the dragon destroys the Brethren's headquarters, killing all but two absent members. At the coronation ceremony, Vimes shouts a premature dragon warning that proves false, and Wonse strips him of his badge. Moments later, the actual dragon arrives, incinerates the High Priest of Blind Io, snatches Wonse, and installs itself in the palace. Through Wonse, the dragon demands tribute, conquest, and a monthly virgin sacrifice. The city's leaders acquiesce in shame.

Vimes deduces that Wonse is the Supreme Grand Master from his distinctive gait, seen fleeing the destroyed meeting house. He infiltrates the palace and confronts Wonse, who has him thrown into the dungeon. There Vimes discovers the Patrician living comfortably: Vetinari has organized the dungeon's rats into a society and had the cell built with all bolts on the inside. The Librarian, an orangutan transformed by magical accident who has been investigating the theft, wrenches Vimes free and shows him a proclamation: Lady Ramkin, the highest-born unmarried woman in the city, has been taken as the dragon's sacrifice.

The Watch positions itself on a whisky distillery along the dragon's flight path. Colon's arrow bounces off a scale, but the dragon's retaliatory flame ignites a thousand-gallon vat, creating a fireball that stuns the creature and sends it crashing into the streets. Vimes reaches the plaza, frees Lady Ramkin by hacking through her chains, and fights off guards while Carrot formally arrests the downed dragon.

Then Errol returns, transformed into a silver-scaled, jet-propelled creature balancing on a stream of reversed flame, the first dragon to flame backwards. He challenges the great dragon, dodging its attacks with impossible speed, then streaks over the plains and breaks the sound barrier. The sonic boom staggers the larger creature, but Errol does not press his advantage. He hovers, wailing. The great dragon responds submissively. Lady Ramkin recognizes the truth: The great dragon is female, and Errol has been courting, not fighting. The two dragons fly away together over the city walls.

Vimes leads the Watch into the palace. They find Wonse with the Patrician, who has already freed himself through secret passages. Wonse attacks Vetinari with the ornate royal sword; Vimes blocks the blow with Carrot's plain blade, which cuts the jeweled weapon in half. Wonse retreats, threatening to summon another dragon. Vimes tells Carrot to throw the book at him. Carrot, taking the phrase literally, hurls The Laws and Ordinances, striking Wonse on the forehead and sending him through a gap in the wall to his death.

The Patrician resumes power. At a formal ceremony, the Watch names its reward: Colon requests a modest pay raise, reimbursement for a kettle Errol ate, and a dartboard. Vimes laughs until he cries. He visits Lady Ramkin expecting a routine call but finds a candlelit dinner and surrenders to the connection between them. On patrol, Carrot mentions his crown-shaped birthmark and plain sword but dismisses their significance, insisting real kings carry magical blades. Colon privately wonders whether a true king's sword might be plain rather than jeweled, but lets the thought pass. The novel closes with Errol and the great dragon as two specks flying off the edge of the Disc into star-dotted space.