(I got a copy from the publisher, in exchange for an honest review.)
3.5 stars. I quite enjoyed it overall.
This novel is a tale of choices gone wrong, of moments that could've been but had to be sacrificed, of events that still left a sad taste even though they weren't that bad at first sight. It's a tale of time travellers that are doomed to meet each other coming from different directions, one gradually gaining insight he wouldn't have had if the other hadn't allowed him to grasp them first, and conversely. It's also a tale of love both doomed and stronger than everything. A rather odd mix, but one that I found intriguing and entertaining.
Time travel here isn't exactly the main focus, although it's the main means. Some of the motivators could be easily seen as self-centered and selfish—and it isn't lost on the characters, who admit it themselves at one point or another. One of the interesting sides of the novel, apart from the science fiction aspect, is that it challenges human nature in several occasions, and you easily find yourself wondering: "What decision would -I- have made, in such circumstances? Can I really blame this character for wanting that?" The scientific concepts behind time travel are never really explored in depth, but somehow, it doesn't really matter. At least, it didn't matter that much to me, because more important than that were the people, the decisions they would make, and how they would manage to cheat the space-time continuum in order to get what they wanted—or had to do to prevent something really bad from happening.
(Granted, when I say that scientifically, time travel wasn't explored a lot, it's not exactly true. We don't get explanations about how the modules work, but the reasoning behind the travels, behind echoes of people being left in the timeline, seemed believable and interesting.)
Another nice part of the book is how it appears as a puzzle, and as a reader, you have to piece things together. Something mentioned in the very first chapters will make full sense only 150 pages later, yet when it finally does, you realise you were right in paying attention.
On the downside, the explanation behind the unhappenings was perhaps a little too simple to my taste, in that I actually wanted to see more of, let's say, what was causing them. Due to the first person point of view, that "adversary" was painted in more dark shades than light ones, and I'm left wondering if things were supposed to unfold the way they did, or if there wouldn't have been yet another way, less dark. I also thought that a few things went too fast towards the end (a certain person breaking down, for instance, as this felt just... bizarre), and that the whole Project might have deserved being mentioned more than just in passing.
Nigel at times seemed somewhat callous—not an unexpected nor unforgiveable trait considering all the unhappenings; only a few events were brushed over (e.g. his feelings regarding his parents), and it was sometimes hard to decide whether he did things out of love and forced himself not to think of the impact on himself, or had just lost the ability to "feel". I guess it's not exactly a defect, as the context justifies it, but at some moments I appreciated it, and at others I didn't. Same at the very end with Helen, whose decision was... I don't know, both understandable and "why on Earth did we do all that for if it was for things to come to -this-?"
However, as said at the beginning of my review, I enjoyed the story nonetheless. It probably also deserves to be revisited to see if I haven't missed anything between the lines.