Anna arrives on Mars and finds a note to herself- in a manner that suggests that she wrote it. The note tells her not to trust the base psychiatrist, something her gut also tells her. As she acclimates to the base other things happen to make her doubt whether she's entirely stable, or perhaps she is suffering from immersion psychosis, a condition that's not uncommon for people making the long trip. Complicating matters is the fact that she has a history with dissociative episodes that go back to an abusive father. This is a huge part of the story, and I could really sympathize with Anna as she went through these tough memories.
The problem I had with Anna is I didn't really like her that much. She has a husband and child back on Earth and I came to appreciate the journey she makes as she confronts her feelings about motherhood, but for most of the book she irked me. But she does ask some essential questions. What is the nature of motherhood? Do we judge women by their feelings on motherhood, on if they're a "good" mother, even though that's only part of who they are?
That's the point of good science fiction, I believe. The best science fiction makes us look at ourselves too, and perhaps rethink preconceived notions. Or just straight up challenge us. This book did that. She also took on religion, it seemed to me- I've read lots of books where religion was frowned on but this one seemed more in your face about it? That may just be my take, I can't speak to what the author was going for there, but I can see where that might be challenging for some.
Part of the problem is there were literally pages and pages of angst, and I thought it was being laid on a little too thick? But I also saw in the acknowledgements that the author has a personal interest in addressing some of these issues, and that caused me to rethink some of my concerns.
So... the ending. Or the last third of the book, which hit me like a gut punch. Seriously, one of the better twists I've had the pleasure of reading. The whole book has this air of mystery, of an impending something- I mean you have a base with only four people and an AI running things, and Anna is having memories or perhaps false memories?- you know something is coming, and yup something is! It's a doozy and I can't say much without spoiling, so I'll just say it works. This book redeemed itself for me in a big way- I still have some issues with all the Anna introspection, not because of her feelings but because it seemed to go on forever- but taken as a whole the book worked for me.
I'd love to see what other people think of Anna and her choices, and also the relationships she forges with the other members of the team. As part of the Planetfall series (I have not read the other books) it is loosely connected, you don't have to have read the others to follow along, although I imagine it adds a lot.