Thief, Liar, Gentleman? By Eleanor Updale.
A YA book, first in a series. I liked it; I'll be reading at least the next book.
The premise was interesting--a petty thief leaves prison and begins a dual life, that of criminal and gentleman. But the character makes too many mistakes for me to consider him a criminal mastermind. He's just too consistently lucky. Underneath it all, he's little better than an animal, barely self-aware.* Knowing there are more books in the series helps; the character can develop. Maybe it was just the way the book was pitched on the cover. I was expecting a criminal mastermind, dammit.
The only major problem with the book was that the middle section dragged to the point I almost put it down. So I thought about it, and I woke up going, "You know what the middle section needs? A McGuffin. Wait, not a McGuffin. A nemesis."
The beginning is great--the process of the character getting out of prison, making the changes necessary to survive in this dual life he's planning--and the ending is better (but I won't talk about that). But the middle doesn't have anything to move it forward. The character just does stuff, without any real opposition. (Well, any real opposition in a fictional kind of way. There are problems, but nothing unifies them.)
There's a detective in the middle with an interesting parallel scene--he and Montmorency are both reading the same article at the same time, and you get to see their different reactions. If the detective had been developed a little earlier, he would have been great way to pull together some conflict for the middle section. A good guy, hard worker, just wants to do his job and not play politics...not especially brilliant, but always just this far away from catching the main character (because Monstmorency isn't all that brilliant, either), until the end section escalates things to the point where Montmorency realizes he's had it relatively easy all along.
Is that a nemesis? A temporary nemesis, a reflection (an opposite) of what Montmorency is at that point of his life, anyway.
The Amazon review recommends the book for middle-schoolers who like Lemony Snickett and Phillip Pullman (and John Bellairs, but I haven't run across him yet), but I'd say it's more of a "If you liked The Mysterious Benedict Society" book.
*Conscience and conscious come from root words for "knowledge."