Amy and her parents are joining an expedition to colonize a new planet, but the trip is so long that they have to be cryogenically frozen. Elder is one of the members of the ship's colony, the people who aren't frozen who run the ship on its journey. When Amy is unfrozen before her time, she is shocked and horrified by the changes she sees in humanity on the ship, leading Elder to discover a dreadful truth about the ship. And when other frozen colonists are found thawing and dead, Amy and Elder must discover the murderer before the entire colony is lost. 
 I don't read a whole lot of YA sci-fi (I think the last YA sci-fi I read was William Sleator's 1980s oeuvre, like Interstellar Pig and House of Stairs), but I thoroughly enjoyed Across the Universe. Usually, stories told from two different first-person viewpoints can get confusing because the author doesn't differentiate the voices enough, but I was never confused about whose head we were in. 
 Likewise, the pacing and clues were pretty much spot on; sure, it wasn't hard to tell who the main bad guy was if you were paying attention, but there were more mysteries happening in the book than just "who's killing the cryos." Lots of smaller things weren't revealed until right near the end, right as I was starting to get really frustrated about not knowing (that's the best time to reveal them, imho). 
 The romance was a bit meh in the sense that these two barely know each other, and their reasons for being attracted to each other are a bit thin, but I've come to expect that from YA (unfortunately) anymore. 
 All of that said, I'm surprisingly uninterested in reading the next few books. I felt that this stood up perfectly well on its own and I don't need to see if they make it to Centauri-Earth or how everyone's going to react to the changes on the ship. I might read them at some point, but it's not a high priority.