Time Trapped, by Richard Ungar (Putnam, Sept. 2013, upper middle grade), is the sequel to Time Snatchers (my review), and continues the story of Caleb, a boy taken from his family and trained to travel through time to snatch treasures at the behest of a sadistic and megalomaniac boss, known as Uncle. The central story is set about 50 years in the future, to allow for the technology that makes the time travel happen, but there is much bouncing between other time periods. And in fact, when Time Trapped opens, Caleb has found a home back in the late sixties, and hopes he has escaped Uncle once and for all...
He hasn't. He is dragged back into Uncle's clutches, and forced to prove his loyalty, along with the other more experienced minions, kidnapping more children from various pasts and places and training them to become time thieves themselves. But Uncle's vicious little empire is not quite the watertight dictatorship it once was. Uncle himself is become less interested in the business of buying and selling the past, and more interested in his own dreams of insane personal power, and isn't there to personally quell resistance among the new recruits; instead, one of the more sadistic kids is claiming power. And Caleb, having tasted freedom, doesn't want to give it up. On top of that, there are hints that the past is more unstable than Uncle had realized, adding a nice dollop of tension to it all (although I felt this problem was introduced, and than left hanging more than I would have liked. Perhaps in book 3....)
And in short, it is a gripping adventure in which the suspense relies not just on completing heists and keeping Uncle happy, but on the efforts of Caleb and his cohort to resist their fate as pawns. Though the ending relies on something of a deus ex machina, it required considerable effort, luck, and cunning on the part of the various kids to get to that point. Because of this more character-centered story, and because there seemed to be more lighter moments (thanks in large part to the introduction of a young recruit who doesn't take nothing from nobody), I enjoyed this one more than the first (which didn't work all that well for me).
The various technologies, and the imperatives of the plot, mean that the cultural complexities of time travel are glossed over, so it's not one I'd necessarily give to someone who enjoys time travel for the sake of the strangeness of it. It's more a series I'd give to kids (ten and up) who enjoy brave young protagonists taking down big bad enemies who are trying to control their lives, with plenty of struggle and desperate action.
I myself still had a few problems with the internal logic of it all, but was able to ignore those doubts and go along for the ride happily enough.