This one's quite dark, and there are all sorts of darkness. Some are dispelled by light, some by truth and some by sheer force of will. Sam Vimes reads a book to his sone every night at 6pm sharp. Comewhat may, he reads "Where's my cow?" complete with all the animal noises. And he never misses it, because if you'd miss it for a good excuse, you'd miss it for a bad excuse, so for this there are no excuses. He stays good to his word, even if sometimes there is a little bit of easing of the path in order to make sure he's always there. There's interspecies trouble in the lead up to Koom valley day, which comemorates the many, many times that the trolls and dwarves have fought each other. There's even a board game based on the species interaction, the Thud of the title. the skill is not to win using your own species, the skill is winning when playing the other side as well. The pieces are moved round the board as the charaters move across the land and it's a close run thing between the truth, light and will power against the dark.