Thud!

'FOR THE ENEMY IS NOT TROLL, NOR IS IT DWARF, BUT IT IS THE BALEFUL, THE MALIGN, THE COWARDLY, THE VESSELS OF HATRED, THOSE WHO DO A BAD THING AND CALL IT GOOD ...'
In the city of Ankh-Morpork, tension is rising between dwarf and troll communities.
A dwarven fanatic has been stoking the flames of an old hatred born of the Battle of Koom Valley -an ancient war between the races that neither side has quite got over. When the dwarf is murdered, with a troll the only witness, Commander Sam Vimes of the City Watch must solve the case before history repeats itself.
With his beloved Watch crumbling around him and war drums sounding, Vimes must unravel every clue, outwit every assassin and brave any darkness to find the solution. But darkness is following him ...
And at six o'clock every day he must go home to read a bedtime story to his son. There are some things you have to do.
'Consistently funny, consistently clever and consistently surprising in its twists and turns' SFX
Thud! is the seventh book in the City Watch series, but you can read the Discworld novels in any order.