Sea of Tranquility follows a series of characters who each encounter, in some way or other, a strange moment which does not make sense with the context of the moments immediately before and after. The book is told in short sections in various times, ranging from 1912 to 2401. 
This book plays with time travel, and the hypothetical repercussions of us inventing it, in an incredibly interesting way. The first three perspectives are of people who encounter the anomaly, and these three perspectives were, frankly, the least interesting to me. I was curious to see how the novel progressed, since I had been told it was really interesting, but the early perspectives did not really draw me in. Once we got to the perspective of Gaspery-Jacques Roberts, I quickly became more interested. I found the time travel, as well as the other changes humanity had gone through, extremely interesting, and I liked learning more about it as Gaspery did. 
I really flew through the second part of this book, and I really enjoyed the final conclusions about the anomaly experienced by these various characters. This was a quick read and one that I enjoyed a lot. I'd especially recommend it if you're intrigued by time travel and the potential implications it could have.