Or the original title, All you need is kill.
So, if you've seen the film, this has the same basic premise. Alien invaders, leads to massive war, but killing one weird type of alien puts the main character, Keiji, in a time loop. In the movie, Keiji is of course, played by Tom Cruise.
In the book, he's a solider in the Japanese Army, in the film, Cruise is basically a US army PR-man. But the same thing happens, he keeps getting killed. They also have fancy exo-skeleton like armour that makes them a bit super human. Eventually he and Rita (played by Emily Blunt in the film) meet and we find out that Rita had previously been caught in a time loop. Because Keiji remembers everything that happened before, he gets better and better at using the armour and being a soldier.
However, the broad plot is a bit different. There is no tracking down the ultimate weird alien Paris for example (in the book there are more than one ultimate weird alien). It all takes place at the same Japanese army base. Also, massive divergence at the end of the book from the film. Let's just say, the movie has a much more satisfying ending.
I'm trying to determine if it was sexist or not. A lot of the characters with actual speaking parts are women, including Rita (nicknamed the Full Metal Bitch) who is super bad ass. However, they are all objectified to a large extent. But they are also really smart (the one is a dietician and the other is a super smart MIT grad who maintains Rita's combat armour). Hmm. Jury's out.
Overall, it is a very short and fun read. The concept is super smart and it's interesting to see how they get around the repetitiveness of the repeated day, either by taking it from someone else's perspective (Rita's in one instance) or having Keiji do something different that changes how that day's events unfold.
I think the movie pips the book because of the ending though, as I found it really sad at the end of the book and a bit of a let down. I suppose this is the problem with watching the film first, they all have more or less happy endings. Anyway, a solid 4/5 stars as I'm still not sure if it was sexist or not.