Basically, there’s a portal randomly scooping people up from across Earth’s history and dumping them in near-future America. The government collects them in a rather benign high-security gulag. When the protagonist, Cate, arrives she falls for a cute fellow prisoner, and they decide to find out what’s going on.
This is very much in the young adult style—first person, present tense, fast-paced plot, some romance, some mystery, nefarious government types up to no good. If you enjoyed Maze Runner and similar, you’ll like this. It’s very well written in parts, very readable throughout with few editing errors.
This is the start of a series, and the ending for this first book is a bit cliffhangery, though it’s still a decent standalone read.