The first book in "The City Watch Trilogy," "Guards! Guards!" is actually the eighth book in the Discworld series by Terry Pratchett. In it the hero of all three novels in this trilogy, Captain Sam Vimes of Ankh-Morpork's Night Watch gives up drinking, gets engaged, and rescues Patrician Vetinari from his own dungeon--well, sort of.
Ancient Ankh-Morpork is as quiet as it ever gets until the Unique and Supreme Lodge of the Elucidated Brethren decides, with a little prompting from its Supreme Grand Master, to conjure up a dragon. The dragon is to cause enough death and property damage (including a vegetable stand with a rude owner and a brother-in-law's shiny new carriage) so that when the Supreme Grand Master's nephew rides into the city with his sharp, shiny sword and slays the beast, the grateful citizens will proclaim him king.
This plot works well, except that the dragon decides that it wants to be king and cremates its would-be slayer. Its requirements are simple and traditional: one well-bred virgin per month, and all of the gold, silver, and jewels in Ankh-Morpork for its hoard.
The only three surviving members of the Night Watch, Captain Vimes, Sargeant Colon, and Corporal Nobbs must somehow slay the dragon and rescue the virgin, who just happens to be Sam's wife-to-be.
The second novel in the trilogy, "Men at Arms" has Captain Sam Vimes at the point of retiring and marrying the virgin he rescued in "Guards! Guards!" The Night Watch itself is becoming an equal species organization with a little prodding from Patrician Vetinari, and Gaspode the Talking Dog falls in love with new recruit, Angua, the werewolf. She has just joined the Night Watch under the Equal Species Act, along with Detritus the Troll and Cuddy the Dwarf.
No wonder Sam, who is a bit of a male chauvinist speciesist is going to retire.
But before he gets his gold watch, Captain Vimes and his command must investigate the murder of Beano, the clown. Sam is also under orders from his wife-to-be to find a missing swamp dragon, which is likely to explode if it comes under stress.
When a large hole is blown in the headquarters of the Assassin's Guild, Sam has a pretty good notion of what caused the explosion. What he really wants to know is whether this latest calamity has something to do the Beano's death. After all, the Assassins are right next door to the Guild of Fools and Clowns.
What he does not yet know is that mad genius, Leonard of Quirm's deadliest invention has fallen into the hands of a rabid monarchist who will do everything in his power to restore Ankh-Morpork's rightful king---and that king is a member of Sam's own Night Watch.
The monarchists are still plotting away in this trilogy's third novel, "Feet of Clay."
Commander Sir Samuel Vimes, of Ankh-Morpork's Night Watch pays a visit to the Dragon King of Arms at the urging of his new wife, who thinks Sam needs his own coat-of-arms now that he's been knighted. Unfortunately, one of Sam's ancestors was a regicide so his descendent is denied an armorial bearing by the College of Heralds. He does learn that one of his watchmen is actually the Earl of Ankh: the inimitable Corporal Nobbs, who is forced to carry around a piece of paper signed by Ankh-Morpork's Patrician certifying that he's really human.
Well, this is a bit of a come-down for Sir Sam, but he's got more important matters on his mind, including the murders of two harmless old men. One of them was beaten to death by a loaf of Dwarf bread. His body was discovered by Captain Carrot and Corporal Angua, the only werewolf in the Night Watch, when they visited the Dwarf Bread Museum on their day off.
The only link between the two corpses is a trace of white clay at both murder scenes.
Subplots zigzag every which-way through "Feet of Clay." Corporal 'Earl of Ankh' Nobbs is being courted by a group of well, nobs who haven't given up on the notion that Ankh-Morpork should be ruled by a king. Captain Carrot, hereditary king of Ankh-Morpork who wisely refused the crown in "Men at Arms," is busy tracking murderers and emancipating golems. Sargeant Colon is about to retire if he lives through a trip through the sewers with Wee Mad Arthur. Corporal Angua helps a new dwarf recruit come to terms with a yen to wear lipstick.
Eventually, all of the story lines tie together very neatly according to character, and the monarchists get their final comeuppance.
This trilogy is a great introduction to Pratchett's award-winning Discworld fantasies, now numbering thirty. If you'd like to read all of the Night Watch novels in order of publication, they are: "Guards! Guards!" (1989); "Men at Arms" (1993); "Feet of Clay" (1996); "Jingo" (1997); "The Fifth Elephant" (2001); "Night Watch" (2002); and "Thud!" (2005).