The basic plot of the novel stems from the final Jesuit mission to Japan in 1643, in which several Jesuit priests apostatized after interrogation and torture by the Inquisitor Inoue. (firstthings.com)
Key truths of Christian discipleship are woven into the plot of this novel: suffering as a condition of following Christ and the hallmark of true charity; the helps that are available to us and the assurance that God never leaves us without help; the truth that God has placed us where we are for a particular purpose, and that He is able to draw good from evil; the truth that no one is doomed to mediocrity, because there is always the possibility of going deeper in one's relationship with God. (faith.org.uk)
The plot centers on Amanda, a woman from modern London, who enters the plot of the novel through a portal in her bathroom and finds herself joining the Bennet family and disastrously changing the course of events. (decider.com)