I'm not entirely sure as I haven't read this specific novel in detail. But generally, it might be about a character named Raeliana who somehow finds herself at the duke's mansion. It could involve her adventures, relationships, and perhaps some sort of mystery or drama within the mansion's walls.
Since I haven't read it thoroughly, I can only assume that Raeliana is one of the main characters as she is in the title. And of course, the duke who owns the mansion is likely to be a main character too.
It could be that there was a hidden agenda or a mysterious force at play. The story could have built up to this point through a complex web of relationships and plot developments.