The King of Arcadia

A romance, in which the romance part is hampered by the fact that He is the chief engineer on the dam that's going to flood Her father's lands. All sorts of shenanigans are taking place. Chief engineers (and others) are dying like flies. The main characters add two and two, get five, decide that Her father is guilty, and reconcile this assumption with the otherwise lack of probability by deciding that he's intermittently insane.