This may be my favorite of all the Father Brown stories. The story is set in Belgravia in a very exclusive (fictional) hotel where a group of gentlemen called The Twelve True Fishermen have an annual dinner. There are a number of real-life, très expensive hotels in that extremely posh area of London which I explored via Google Maps (the Berkeley, the Emory, the Wellesley, the Lanesborough, the Peninsula, the Cadogan, etc.) and that enhanced the atmosphere of the story.
The hotel’s chef prepares an abundance of gourmet dishes featuring fish and the diners use a special set of silver fish knives and forks, each of which is inlaid with a large pearl.
Father Brown is present at the hotel only because one of the waiters had a stroke and requested a priest. After seeing the fatally stricken waiter and administering last rites, he asks if he can be taken to a private office to write a note on behalf of the waiter. While in a tiny hole of an office he hears very odd footsteps - a series of running steps followed by slow, regular ones.
Father Brown has solved a very unique robbery before anyone else even knows a crime has been committed. Or, as Chesterton puts it: “… he had averted a crime and, perhaps, saved a soul, merely by listening to a few footsteps in a passage.”