Books like The hidden ruin by Franklin Folsom

Our story begins when Charles Belton (who made his first appearance in The Headmistress) is hired on as a junior master at Philip Winter’s Priory School. This serves mostly as a means of crashing together all sorts of young people from Thirkell’s earlier books, who might otherwise have remained isolated in separate corners of Barsetshire, and making as many romantic matches as possible. Thirkell has gathered together Lucy and Oliver Marling, Charles and Freddy Belton, Susan and Jessica Dean, Colin Keith…every unmarried youngish person of note shows up, mostly (in the case of the men) to flirt with Jessica Dean. Even the too, too precocious Clarissa Graham gets to try her hand at flirting with Captain Freddy Belton, though he is thirty-five to her eighteen.

When his archaeologist father disappears, fourteen‑year‑old Will Burrows discovers a tunnel that leads to a subterranean city called the Colony, revealing hidden family ties and a world of underground adventure.

"I very much need to be dead." These are the chilling last words left by a man who had everything to live for but took his own life. In the void that remains stands his widow, FBI agent Jane Hawk, surrounded by questions destined to go unanswered unless she does what all the grief and fury inside her demand: Find the truth, no matter what. People of talent and accomplishment, people seemingly happy and sound of mind, have recently been committing suicide in surprising numbers. A disturbing pattern is beginning to emerge. Jane is determined to give up everything to find out why. And if that means going rogue and becoming America's Most Wanted, then so be it. Those arrayed against her are legion, and devoted to protecting something profoundly important-or terrifying-enough to exterminate any and all in their way. But Jane is as clever as these enemies are cold-blooded, as relentless as they are ruthless. And she is driven by a righteous rage they can never comprehend. Because it is born of love.