As with many works of fiction aimed at Young Adults, there are no real surprises here. The plot arcs are all somewhat obvious from the start. The coincidences all line up too well and seem far too coincidental for my tastes. And, although Eleanor experiences some of the pain of war --she learns of the murder of her Jewish relatives in Europe by the Nazis, her soldier boyfriend loses a limb, etc. -- everything works out relatively well in the end. So, I won't worry about "spoilers" and will instead just tell you about some relevant information about the book:

A major plot point is the trauma Eleanor experiences as a young girl when her father -- a math professor -- has a stroke which leaves him severely disabled. Since she (mistakenly) blames herself for this, she refuses to acknowledge her own mathematical abilities which she feels she does not deserve.

At first, she hides the fact that she can do math from everyone. But, after being "discovered" at a math competition when she is the only one able to evaluate an antiderivative using the method of partial fractions, she accepts a job working at a secret government facility. From this point on, her mathematical skills are recognized and utilized by the military, but she continues to keep it a secret from her family until near the very end.

Eleanor's first job is to be a computer (in the original sense of that word, as a profession for a human rather than as w machine). Specifically, she was working out the trajectories for different combinations of weapons and ordinance which were compiled into tables and used by soldiers for the purpose of targeting. Eleanor later also uses her mathematical abilities to fix an analogue mechanical computing device designed to numerically integrate, manually works out the effects of turbulence to better target bombs dropped from planes, and eventually even goes on a critical bombing run herself. I don't honestly know enough about how mathematics was used during World War II to know for sure if those are things that people actually did, but it all sounds reasonable to me. (The afterword listing certain details and characters from the book as being factual indicates that it was well-researched.)

This book is good propaganda for the field of mathematics in that it shows it to be both interesting and vitally useful. Also, it is good that a variety of different types of people are presented as mathematicians (including a Black woman).

On the other hand, there were some mathematical details which I found annoying and difficult to swallow. When Eleanor is first presented with a Marchant Calculating Machine she tests it out by computing 355/113 which it finds to nine decimal places. I would be a bit surprised if a mechanical calculator could compute that to nine places after the decimal. (I don't think those early mechanical calculators behaved like our current electronic ones, only more slowly. Does anyone know if that is realistic?) But, I am absolutely certain that (contrary to what the book says) 355/113 is not the (irrational) number π!! Another thing that annoyed me was the repeated description of "x+1=x" as "the equation for infinity". (I'm not sure, but I am guessing the author is referring to the fact that there is a bijection between any infinite set and itself with a single element added. Indeed, that does mean that a transfinite cardinal is equal to its own successor.) Eleanor is the sort of stereotypical math nerd character who thinks of formulas or obsessively counts things around her searching for prime numbers whenever she is nervous. Perhaps there are people like that. (Was Ramanujan one? I don't know.) But in any case, they are way over-represented in fiction IMHO. Finally, I found the seemingly "magical" way in which Eleanor seemed to do math to be annoying. Rather than thinking about it, she seems to just "see" it. I sometimes think that this sort of "visual" math is something that was invented for portraying mathematical genius in movies and TV shows, and I worry that it will leave people who actually have to work it out with the mistaken impression that they could never really pursue a degree or career in mathematics as a result.

I hope my complaints above (about the way math is represented and about the unsurprising plot) do not sound overly critical. In fact, I did enjoy reading this book. I liked the characters, I felt bad for them when things did not go well, and was rooting for them to succeed. So, I can recommend it to others. But, I do think that it would be best suited for a young audience.