Guards! Guards! by Terry Pratchett

Yea, the king will come bringing Law and Justice, and know nothing but the Truth, and Protect and Serve the People with his Sword. - Old Discworld Prophecy

Be careful what you wish for.

The eighth installment of the Discworld series is set in the ancient city of Ankh-Morpork.  It has been centuries since the city had a monarch, being ruled currently by a Patrician, Lord Vetinari, a tyrant in all but name.  A certain secret society is unhappy with this state of affairs and they hatch a plan to take control of the city by setting up a puppet king.  But they get much more than they bargained for.

Taking riffs from the film noir and noir literature genres, plod-police shows and combining it with Discworld magic, Pratchett provides us with a gumshoe/police mystery.  In doing so, and in the first of the Night Watch novels, he introduces the utterly memorable characters of Sam Vimes, Fred Colon, Nobby Nobbs, Carrot, Lady Sybil Ramkin and C.M.O.T Dibbler.

Thematically, Guards! Guards! is about human nature and the tendency of ordinary folk to allow evil to flourish through inaction and fear, rather than through intrinsic malice.  It also explores the phenomenon of humans abdicating their moral responsibility en masse to those in supposed positions of authority.

Of course, Pratchett's genius (apart from character creation) lies in his ability to take a serious theme and leaven it with sparkling humour - and there is a lot of humour in this novel - to make it more palatable, provoking thought and laughter at the same time.  A rare talent, indeed, and one to be all the more relished for both its rarity and its acuity.