Confinement is split between two loosely intertwined stories taking place at the same school, roughly 150 years apart. As other reviewers have suggested, the effect of alternating back and forth between the two can be jarring, but both tales are at least somewhat compelling nonetheless.
Bess Hardemon, the heroine of the 19th century portion of the story, is truly a five-star achievement of character development. Like many pioneering real-life women of her era, she sounds positively anti-feminist by today's standards, but that belies the real progress she made for the girls of her generation and those since then. She and most of her family and colleagues ring absolutely true to anyone who has studied the history of the era, and I found myself rooting for her to win all her reforms. The tale does occasionally take the easy way out, but that is forgiveable in such a well-developed and readable story.
In the modern half of the story, Sarah Beckett and her friends are both a bit less developed and a bit less likeable. Some of the more dramatic twists in her story, while vividly written, are a bit hard to accept. For example, her reaction to being dumped by her first boyfriend, while plausible for many teenage girls, seems a bit extreme for one as mature and well-adjusted as Sarah is portrayed as being early in the story. Her continued obsession with the man in question later in life may also strain your ability to be sympathetic after a while. Sarah's friend Imogen is a bit more convincing as a character, but her career path as an adult is wildly implausible given her early history. Some of the subplots are also rather underdeveloped as well, notably that of the link between the Bess Hardemon era and the current one. It's a good start, but a lot more could have been done with that particular tangent.
Still, it's definitely an enjoyable read for anyone who likes historical fiction or coming of age stories. Confinement is both for the price of one!