The title refers to the Dwarfs vs Trolls board game, played like a cross between draughts and chess. (Did you know there's an Oriental game called shogo which is like chess, but the captured pieces play for the opposing army? Sounds like fun).

    It hadn't always been like this. Things had loosened up a lot in the last ten years or so. Dwarfs and trolls as races would never be chums, but the city stirred them together and it had seemed to Vimes that they had managed to get along with no more than surface abrasions.
    Now the melting pot was full of lumps again.

The latest City Watch book seems to be the darkest of them all - the darkness that dwells deep in dwarf mines, and comes out when dark and evil deeds are done. Deep in the mines, trapped in close communities and never afforded privacy, dwarves have developed dwarfsign, an ideogrammatic graffitic safety-valve that releases pressure when emotions and tensions are ready to explode. And one of the worst of these signs is the Summoning Dark, which has started appearing in places it has no right to be...

One of the most important grags (religious leaders that dwarves don't have) has been stirring up hatred against the trolls, it being the anniversary of Koom Valley, the great battle between dwarfs and trolls that seems to have happened repeatedly throughout history, in which both sides were ambushed simultaneously, possibly yelling "Remember Koom Valley!" as they did so. Except now it wants to be refought on the streets of Ankh-Morpork, just when Vimes has too many other problems to worry about.

   ... it was so much better when there were just four of us up against that bloody great dragon, Vimes thought as they walked on. Of course, we nearly got burned alive a few times, but at least it wasn't complicated. It was a damn great dragon. You could see it coming. It didn't get political on you.

Politics is now Vimes's biggest problem - instead of fighting crime, which is his first priority. The Black Ribbonners are pushing to have a vampire in the Watch (and Vimes is running out of excuses), the grag causing all the troll-on-dwarf-and-vice-versa violence may or may not have been murdered, and the murderer may or may not be a troll. The biggest problem, of course, is for Vimes to get home every evening at precisely six o'clock, for Storytime with Young Sam.

   It was the same book, every day. The pages of said book were rounded and soft where Young Sam had chewed them, but to one person in this nursery this was the book of books, the greatest story ever told. Vimes didn't need to read it any more. He knew it by heart.
   It was called Where's my cow?
   The unidentified complainant had lost their cow. That was the story, really.

It's all in a day's work for his grace his excellency Sir Samuel Vimes (knight, blackboard monitor and Commander of the City Watch). In fact, in order to stop Koom Valley happening in Sator Square, Vimes has to follow the trails not only of grag Hamcrusher but of the mysterious Mr Shine, a name turning up as troll graffiti all over the city. Vimes secretly suspects it's some brand of ovencleaner no one's ever heard about. The only clue is the painting done by the painter Methodia Rascal. It took him sixteen years to finish, and ultimately drove him mad. (Either he thought he was a chicken, or that a chicken was trying to kill him. Either way, he was found dead and covered in chicken feathers. He left several insanely-scribbled notes that might be clues, or might just be chickenscratch).

   I think I'm looking at this wrong. It's not my cow. It's a sheep with a pitchfork. Unfortunately, it goes quack.

Yes, a fully fledged takeoff of the DaVinci Code, with the site of a secret treasure hidden in the painting. There was a book about it, possibly called the Rascal Codex, I believe, although unfortunately the entire massive painting's been stolen. By either dwarfs or trolls, Nobby isn't sure.

The author seems to feel that if people just get around the table and talk to each other, all their differences will disappear along with long-standing hatreds and misunderstandings. And while a large part of me agrees eagerly with this idea, another large part knows that human nature cannot be changed, even with a big stick. Chance may be a fine thing...