Dodger tells the story of a street urchin living in London in the early Victorian era. Yes, he's that Dodger - the Artful Dodger, friend of Oliver Twist, pupil of Fagin. But you won't find Oliver here or any of the dancing urchins from the musical Oliver. Dodger makes his living not picking pockets but picking through the sewers of London, looking for treasure. What he finds, of course, is trouble.
When Dodger comes to the aid of a young woman he sees being savagely beaten in the streets of London, he becomes entangled in international espionage, political intrigue, and just plain old murder. He also encounters mass murderer Sweeney Todd, politician Benjamin Disraeli, and a dubious writer named Charlie Dickens.
Pratchett did significant research for this book, and he paints a picture of early Victorian London that's pretty grim. London at this time had no real social safety net and policing was in its infancy. It's not a safe place, and it takes someone like Dodger to survive and thrive. Although the world is grim, Pratchett's usual acerbic wit and Dodger's irrepressible character makes this book a compelling read. The slight fantasy component in no way detracts from the historical setting. I'm only sorry there won't be a sequel.
For similar stories, try The Accidental Highwayman by Ben Tripp or Drood by Dan Simmons, which also has a Dickens connection.