Picking up right where the previous book left off, Sent kicks off the actual time traveling portion of the series by stranding viewpoint character Jonah and his friend, Chip, in the 15th century. See, Jonah and Chip (and about thirty other kids) aren't originally from the 21st century. Each of them was born in another time, and whisked away as "endangered" children to be adopted in the future. And now, they're all supposed to be sent back to their original times, to meet their original fates.
This is not the most favorable plan for Chip, or for fellow time-displaced adoptee Alex: they're the missing princes who may or may not have been killed by Richard III, and they've been returned to the night of their disappearance. Naturally, Jonah wants to stop this from happening, and get his friends back to the time they grew up in.
I read the first book in this series some time ago, but I remembered enough to keep up. It helped that this particular book was very, very slow. There's a lot of talking about what's going on around them, in great detail. Not just about the historical subjects, but also about the mechanics and principles of the form of time travel used here. In some respects, that's fine. Haddix has obviously put a lot of thought into her history and science fiction. I liked her idea of "timesickness": every molecule in your body has existed in some form from the dawn of time, so when you travel backwards or forwards in time (say, 500 years into the past) your molecules are actually meant to be somewhere else. The side effect is that it makes you feel terrible. I can't recall ever seeing this idea before, and Haddix sold it. I also liked the idea that the time travelers (and only the time travelers) can see echoes (called tracers) of what would have happened in the original version of the timeline.
But this is where me not being the target audience for the book comes in. I go into this series with a pretty decent background knowledge of history and how time travel generally works in SF. So the long, detailed explanations of what's going on, both in a historical and science fictional sense, are tedious for me. If I had read this at twelve or thirteen, when I didn't already know exactly what was going to happen to Chip and Alex's original selves, and if I didn't need somebody to patiently explain paradoxes to me, I think I would have enjoyed this book a lot more. Even welcomed the long explanations.
I also feel like the general premise, that the children need to be returned to their original timelines, is never adequately explained. Why
do they need to be returned? What's purpose will be served, versus everything staying at the new status quo? Especially since meddling with the timelines again couldn't possibly return time to its "original" state. Then again, this is a long series, and the first trip is a bit unplanned, so maybe an explanation will come later on in the series. I just don't think I'll be sticking around to read it.