It serves as a great stage for red herrings. An old inn naturally has quirks: strange portraits, family heirlooms with stories, odd architectural choices. The author can plant a dozen details that seem significant because of the setting's inherent antiquity, but only a few are real clues. A hidden drawer in a desk feels plausible there. A mysterious locket found in the garden fits. The setting legitimizes a whole toolbox of mystery tropes that might feel forced in a modern apartment building. It gives the author license to be delightfully theatrical with the clues.
The societal roles are interesting too. You have young women running a business, an elderly woman being taken advantage of, a handsome but suspicious handyman—it's a snapshot of expected and subverted roles in that era. Nancy, of course, subverts the biggest role of all: the amateur detective in a man's world.
It's all about performance. Think of it like a theater production where the inn is the stage. Every guest is an actor playing a part, and the staff are the stagehands keeping the illusion intact. The mystery begins when someone forgets their lines or a piece of the set malfunctions. The theme of identity is explored through the rigor and exhaustion of maintaining a performance 24/7. What happens to the self when the curtain can never come down? The deception is less malicious and more desperately existential for most characters.
The pacing of the middle chapters is noticeably altered. The original had a 'saggy middle' with some filler adventures that were likely cut for the revision. The revised book moves more briskly from clue to clue, with fewer detours. This was probably a smart commercial decision—keeping a young reader engaged—but it sacrifices some of the leisurely, episodic charm of the older style of children's serials.