3.5 StarsConfusing, exciting, and fun, Undercurrent is a novel that readers will enjoy! The story isn't perfect, it has some problems with the secondary characters that makes it a bit tough to like them. But it's a fun story about alternate realities and how one choice can make or break you. Literally. While we're learning more and more about Cal, the writing for the story is more telling instead of showing during the first half. In the second half, the writing gets better, with more things being showed rather than told and it's smoother. It takes Cal longer than it should to figure things out and come up with a plan. The secondary characters in Undercurrent feel quite stiff and boring, they don't stand out or grabbed my attention. Also I wish that some characters had a much bigger role than they had, like the teacher and what makes him so special.Even though Cal does take some time to figure things out, I love his character. He's very sweet and caring and persistent, especially when it comes to his friend, Willow. Somewhere during the middle of the story, things start to pick up and start to happen, people get hurt and tension is thick in the air. And by the end of the novel, everything is so intense it's crazy! Paul Blackwell does an amazing job describing the ending of the story. He gives readers a well-developed back flash and explanation as to why Cal's life has been turned upside down and a killer cliffhanger to end everything off.Undercurrent is a fun ride. The ending is left open and it's exciting, the idea of alternate realities is a creative idea that I really enjoyed. I recommend this to anyone looking for a new science fiction novel or something different in the YA genre. I can't wait to read the next book!