Ship Breaker (which I enjoyed). I was a little disappointed because I was looking forward to Bacigalupi's excellent adult sci-fi, but his YA books are similarly engaging: strong world building, interesting characters, and lots of action.
The Drowned Cities feels a little less sci-fi than Bacigalupi's earlier works, primarily because so much of the book is drawn from real life in its depiction of a nation's chaotic civil war and use of child soldiers. The protagonist of the novel is Mahlia, an orphaned child of a Chinese peacekeeper (though the peacekeepers have long since abandoned the Drowned Cities) and a local woman. Her only friend is Mouse, another orphan who saved her when one of the warring armies cut off one of her hands. When Mouse is taken as a soldier, Mahlia is determined to rescue him, and she attempts to do so with the help of Tool, an enormously strong and dangerous part-human, part-animal augment (and a recurring character from Ship Breaker).
I taught the nonfiction book A Long Way Gone, about child soldiers in Sierra Leone, to my seniors this year, and it's scary how much of Drowned Cities echoes the real life horrors children in such countries have faced. Bacigalupi skillfully shows how such armies indoctrinate their young soldiers, making them feel like part of a team--and ensuring they have no other options.
Tool is probably the most interesting character in the novel, though by the end he felt somewhat unexplored. He's a killing machine on his own for the first time and making real decisions in his life. I like that he's both able to break free of some of his conditioning and show compassion, but that he's also not able or willing to "switch off" the violent part of him--it's who he is, and he accepts that. Mahlia and Mouse serve as good counterparts to each other, and Bacigalupi is even able to make the characters' "why in the hell would they do that?" moments (which are apparently necessary for tension-driven YA) seem believable.
I don't consider myself especially squeamish, so I was a little surprised that one of the most off-putting aspects of the book for me was its intense violence. There is a large amount of graphic and brutal violence done to children and adults, including murder, mutilation, and torture. The violence is realistic in context of modern child soldiers, but it could be strong stuff for the younger end of YA. Nonetheless, Drowned Cities is a worthy companion to Ship Breaker.