Before I start, I'm gonna disclose a bias here: I love dystopias a lot, and I love them even more when the thing that makes them dystopian is the world itself becoming scary and hostile. Really big storms driving civilisation underground... This book would more or less have had to go out of its way to make me hate it.
Some Fine Day does not do that: it's creative, fast-paced YA fiction, and the twists and turns in the plot genuinely surprised me. I admit I was sceptical for the first chapter: Jansin, the main character, is in training to be a secret agent, and I thought I could guess the trajectory the plot was going to take from there. I couldn't, it turned out. Jansin's journey across her ruined earth was unpredictable without feeling random, fast-moving without feeling like you're missing out any key details.
Jansin feels like a plausible creation of the world she grew up in, too. She's suspicious of the world around her but touchingly fond of the few adults she trusts, and this starts to make more and more sense as we learn about her underground city. Some details about it seem a little mawkish (I wasn't as convinced by the state TV channel as I wanted to be) but it's a well-considered setting, and as I got to know it better I really felt for this sad, lonely, narrow world underground, and for the people growing up in it in a culture of deep paranoia.
Our protagonist is very much a product of her culture, and equally very much a teenager: she's frustrated by the narrowness of her world but confused when it widens; she's confident in her fighting skills but nervous as hell about some other kinds of battle. Jansin's been taught to value her martial arts/secret agent skills a lot, but she makes friends with people with other strengths and learns from them. Some of the writing I liked best in the book was about that: tentative friendships forming across a broad culture gap.
This isn't a comment I've had very often, but the men in the book came across as the least rounded characters to me, and Jansin's relationships with them the weakest bits of storytelling. The women all have convincing inner lives - even seen through Jansin's eyes in the book's first-person narration. In contrast, Jansin's ex and her dad seemed to be following a script without putting much energy in, which makes a few key conversations at the start of the book less engaging than they should have been.
They're a fairly minor part of the book, though. The way societies react to their storm-ridden world are a much bigger part of the story, and those are subtle and considered and totally credible.There's a lovely depth of detail about the two different cultures we see in the book, and these differences are wound into the narrative without ever slowing down it down. The only information that isn't part and parcel of the plot are the little snippets of a banned book that start each chapter. These give a history of the disaster, and it has a wonderful way with words:
The hole we dug for ourselves was so deep as to be barren of all life beyond what we brought with us. The long term evolutionary implications of this are, of course, unknown.*
I spent a few trips to work happily theorising about this world over the first half of the book, and then I got to a key turning-point in the plot and ended up reading the rest in one sitting: Kat Ross executes the spy thriller plot she promises at the start incredibly deftly, and not at all the way I'd expected. On those grounds alone I'd very happily pick up a sequel to find out where it's going, and how many motorbike chases and dramatic martial arts fight scenes and near-death experiences it's going to take Jansin to get there. Even without that, though, if an ecologically-triggered dystopian future appeals, and you're the kind of person who enjoys slowly piecing together the history of a disaster, there is a lot here for you.
*(Loc. 3937-8 in the Kindle edition).