This book is the reason I rarely leave a book unfinished.
I almost gave up on this one. I was not invested, the storyline and timeline kept changing, leaving characters behind, I could not find the connector. Because I was not supposed to. Until literally about halfway in.
Then it was: Oh, wait, what? And then: OOOOoooohhhhh!!!!!!!!!!!!!!!!
I read the second half twice as fast as the first half. Natch.
This story is very complicated, and echoes back to several other novels I have read, one of them very recently, which left me in a bit of deja vu. Interestingly enough, in the acknowledgements the author lists about a dozen other novels you should read if you liked Sea of Tranquility, and the books I had in mind were on her list. I won't name them here, as that would be kind of a spoiler. IYKYK. (And I would add the book Replay by Ken Grimwood, one of the best time travel books I have ever read, outside of Outlander o'course, and 11/22/63 by Stephen King).
I am not going to attempt to give you a plot summary here - get that on Goodreads for what it will be worth for this one. I do understand from Goodreads Questions that if you read The Glass Hotel first, you will recognize several characters from that book in Sea of Tranquility. I am hoping that once I go back to The Glass Hotel, I will find out the answer to one main question I felt was left unanswered in a secondary plot about a lesser secondary character (Vincent). Mandel again weaves in Shakespeare, art, a pandemic, and futuristic devices (like she did in Station Eleven). If you like science fiction, the idea of what life could be like in the future, and coming full circle, this is a great read. Be patient, I promise it will deliver.