This may actually be my favorite book from Pratchett that I've read (and I have read quite a few).
I loved it even though it features a large number of historical characters (like Charles Dickens), a feature which often annoys me, if not done 'just right.' Although not without Pratchett's trademark humor, this is a somewhat more serious historical piece than most of his output.
'Dodger' is a young man just growing out of being one of Victorian London's street urchins. He lives with Solomon, an elderly Jewish watchmaker who has more in his past than one might expect.
Dodger ekes out a living by garbage-picking down in the sewers. But when an impulse drives him to come to the aid of a young lady being assaulted in an alley, he unexpectedly finds himself enmeshed in a chain of events that will open doors to him.
Fun adventure-mystery with plenty of twists and turns and vivid setting and characterization. However, I'm deducting one star for far too much harping on how everyone should have empathy for a serial killer because after all, he was just a traumatized individual himself. No, sorry. Pratchett may believe this, but I don't think that reasons are excuses. Dodger should save his charity for victims, not murderers.
But, even with that one quibble, I'd still highly recommend the book, and not just for the YA audience it's being marketed to, either. (I didn't find it to be particularly YA at all, although it does have a bit of a 'growing up' theme.)