Grace Burrowes' "Trenton, Lord of Loss" (#10 in the Lonely Lords series)

Nice story, some really lovely scenes between the main characters, the widow Ellie Hampton and her widower neighbour Trenton, who is the older brother of the main characters in the first two books in this series, Darius and Leah. Even the "suspense" subplot (somebody is trying to murder Trenton!) kind of makes sense.
But - don't try to read this book without having read at least one of "Darius, Lord of Pleasures" or "Nicholas, Lord of Secrets" from this series. There is a LOT of reference to events and people from those books in this one and I think that if you haven't read those, you could feel rather lost in many places in this one, particularly in the chapters with Trenton's brother Darius and with the dreadful father of the three siblings, the Earl of Wilton.
It might also help to have previously read one of the books in the series involving Heathgate ("Gareth, Lord of Rakes") or Greymoor ("Andrew, Lord of Despair") because the characters from those books also appear a lot in this book in connection with the investigation of the murder plot against Trenton. But you don't need to know the background stories from those books to make sense of this one.