I always love time travel, but best of all is time travel that hangs together in a cohesive way, with deep world-building and attention to what time-travel can do to timelines. This book really manages that. I also appreciate the ending, though it feels...hard to take, a bit. You'll see what I mean. I only didn't give it 5 stars because there wasn't much in the way of plot, and also the sidekick got less limelight than she deserved.