We meet protagonist Denise at an animal shelter where she works (or volunteers? works, I think) taking care of cats, including special needs kitties. Denise is 16, and the end of the world is nigh. It's July, 2034, and a comet is on its way to make catastrophic contact with Earth. People make plans, shelters are organized, the rich make better plans, and shuttles to twin planets are launched.
Denise, her substance abusing mom, her absent father, and her coming-back-soon sister Iris are not among the rich, and do not have a place on any shuttle...until they luck onto a "generation ship," at least temporarily. Things ensue.
btw Denise is autistic and really would rather hang around with cats all day, but when the planet is done for, that's less of an option, and Denise, with only her unreliable mother around, has to find her a way to survive.
Denise, her family members, and the people aboard the Nassau are complex and real. Author Duyvis is herself autistic, so presumably she portrays Denise in a way that many autistic and otherwise disabled people will appreciate? I hope so. As a neurotypical lady, I think she nailed us.
Denise and her sister Iris are of color, and Iris is trans. There are other characters of marginalized identities, so Duyvis is clearly trying to keep things real in her future dystopia.