Guards! Guards! - Terry Pratchett

"As traumatic as it is to only choose one Pratchett, this first entry in his Guards sub-series encompasses everything that is brilliant about his writing: terrific characterization and plotting, a completely believable world, and new details that come up with each re-reading. . . . The story of dwarves, dragons and good police work remains fresh, sharp, and incredibly funny." — Telegraph (UK)
Magic, mayhem, and a marauding dragon combine for extraordinary fun in this brilliant Discworld novel from New York Times bestselling author Terry Pratchett.
Insurrection is in the air in the city of Ankh-Morpork. The Haves and Have-Nots are about to face off. Again.
It's old news to Captain Sam Vimes of the city's ramshackle Night Watch. But this time, something is different—the Have-Nots have found the key to a dormant, lethal weapon that even they can't fully control, and they're about to unleash a campaign of terror on the city.
Long believed extinct, a draco nobilis can now be seen patrolling the skies above Discworld's greatest city. Not only does this unwelcome visitor have a nasty habit of charbroiling everything in its path, but it's also soon crowned King.
Can Vimes, Captain Carrot, and the rest of the Ankh-Morpork City Watch restore order (before it's burned to a crisp)?
The Discworld novels can be read in any order but Guards! Guards! is the first book in the City Watch collection.
The City Watch collection in order:

Guards! Guards!

Men at Arms

Feet of Clay

Jingo

The Fifth Elephant

Night Watch

Thud!

Snuff