Curse of the Night Witch, by Alex Aster

Curse of the Night Witch (Emblem Island #1), by Alex Aster (Sourcebooks, June 2020), is a single-sitting, very satisfying middle grade (9-12 year olds) fantasy, with the only unsatisfying part being that the second book isn't available right now.

Everyone (or almost everyone) born on Emblem Island has a mark that shows their particular gift, and a lifeline that magically shows the highs and lows to come, and how long that life will be. Twelve-year old Tor isn't happy with his long, boring life line, that promises no excitement, and downright hates his leadership emblem. He doesn't want to be leader, and doesn't want to spend his days studying the dry texts of leadership education. He desperately wishes he had an emblem for water breathing isntead--underwater is where he is happiest.

At the annual New Years celebration, all the islanders throw wishes into the bonfire, and some are granted. Tor's wish is one of those. The next morning he wakes up with his leadership emblem gone...but now there's a curse symbol in its place, and his life line is shortened almost to nothing. Then his best friend Engle, and his not-friend, Melda (the only other leadership marked kid in his village), get contaminated by the curse. Now they too have only a few weeks to live.

The only way to rid themselves of the curse is to find the legendary Night Witch, who haunts the island's stories, gathered together in the Book of Cuentos that the kids take with them. Those stories are their guides to the fearsome dangers of magical creatures and treacherous terrain outside their home village. The island is bigger and more wonderful and horrible than they had dreamt, but they keep going, and learn to trust each other, and the stories. (And they get home safely in the end, with the immediate problem solved, but new dangers and challenges looming--I can't wait for the next book!).

All the things that make middle grade fantasy adventure so much fun to read can be found here. There's wildly extravagant world-building that somehow managed never to tip me out of the story in disbelief, solid friendship between the kids (including the antagonist to friends relationship of Tor and Melda), bravery (bolstered by lots of help from grown-ups along the way, which I appreciated), thought-provoking considerations of destiny, and a much more nuanced final confrontation than I'd been expecting! The stories in the Book of Cuentos are rooted in tales told to Alex Aster by her Columbian grandmother, which makes the book even more appealing.

Personally, something that made this interesting to me is that it's not a portal fantasy, but a fantasy quest carried out by insiders to the magic of their own world. I think this helped make it feel tight and contained, and helped keep the pacing brisk.

I'd recommend it to fans of the  Morrigan Crow series--totally different setting, but a similar playful feel to the magical setting (although possible I'm thinking about Morrigan because she was "cursed" too...but I think it's a good recommendation nevertheless).  It also felt like one for anyone who enjoyed Lalani of the Distant Sea, and basically one for anyone who likes magical monsters and kids with magical gifts!

short answer-- a really strong series start that I enjoyed lots.