This book is labeled as a mystery, but it's actually a historical romance set during the American Civil War in April 1863 in New Orleans. There is a murder that remains unsolved until the end, but it's not the focus of the story and, since the murderer isn't even known to exist until the big reveal by the murderer's accomplice, it's not really a mystery the reader can solve.
It's a fairly typical "sweet" (no explicit sex) romance novel. Marcy, the heroine, is naive and not very perceptive but she is likable. The hero is gallant, competent, and true even when betrayed by Marcy. There was some nice detail about what living in New Orleans was like at the time, but there were some other (practical and historical) details that I know were wrong. Overall, it was an enjoyable novel.