I would consider this book part of an unnamed series. There's a prequel, The Vow that precedes this book. Rosemarie is considering three knights in this book. The fate of the other two knights is explored in two other books, A Daring Sacrifice, and For Love and Honor.
It's only a month before Rosemarie's 18th birthday when an old family friend shows up and tells her that her fate could be different. When her parents died, she found out she'd been chosen to be a sacrifice to God and would enter the convent on her 18th birthday. Her friend, the duke, tells her that if she marries before that time, she'd released from the vow.
Derrick is one of the knights, but he doesn't feel worthy and doesn't want to compete with his two best friends for the hand of the young maiden. It's clear that she prefers him, but he holds back for a long time. Dangers threaten the contestants as well as the people Rosemarie is supposed to protect.
The book is written in first person, which makes the first half of it predictable and somewhat boring. Being inside the mind of a 17-year-old discovering her feelings of love was a bit much. Every once in a while, we get to read from Derrick's point of view. At first, his chapters are so far apart that I wondered why they were in there at all, but toward the end, more chapters included his point of view, and I was able to engage in the story itself and less with Rosemarie's struggle with her feelings. And the end was just weird.
Overall, if you're looking for a straight up romance, complete with fluttering stomachs and confusing feelings, then I recommend this book. For me, it was too sappy, and I wish there had been more balance between the points of view. Sadly, not for me.