The Daughters of Mannerling is somewhat darker than the other two Marion Chesney series that I've read. Yes, even compared to all the murder and mayhem in The School for Manners. I think the difference is in the sense of maturity. While DoM does contain elements of a comedy of errors, it foregoes the zaniness present in TSoM.
The next eldest daughter, Jessica, is convinced that she will be the one to regain Mannerling. As is the rest of the family still at home. So convinced, in fact, that their naked ambition leaves them open to ridicule, particularly on the part of the Deverses, the family currently in possession of Mannerling. To make matters worse, their son, Harry, is not exactly a catch. He's kind of like a party girl. The really destructive kind.
Possibly more so than the last book, The Intrigue focuses on the almost supernatural power that Mannerling has. Jessica meets the Deverses' nephew Professor Robert Summerville, and with surprising swiftness, he convinces her that Mannerling is just a place, and she should accept its being beyond her grasp. Jessica swerved between letting go of Mannerling and chasing after Harry with Mannerling in her sights.
Once again, Barry the odd jobs man is a force of good on the side of more or less fighting Mannerling's dreadful pull. But this time, he is joined by the mysterious governess Miss Trumble. Much is made of her extraordinary focus on education and little hints that she is more than a "mere" governess. She speaks too freely with Mrs Beverly, and holds herself like a queen.
She's to thank for Robert even noticing Jessica. He spoke to Miss Trumble first, and the fact that she forced the girls to dramatically expand their education was one of the things that made Jessica attractive to him in the first place. I liked that.
I did think that Jessica's romance was rather like Isabella's, but they did have differences. Even if they weren't, it was a nice romance the firs time, and these books are short enough that I honestly forget a great deal even a day later. This makes them eternally renewable! :)