A detective pursues a murderer through a city that might be Buenos Aires, following clues drawn from Kabbalistic mysticism. Borges, who called detective fiction a form of metaphysics, constructs a trap so elegant that its victim collaborates in his own doom. The story is brief, dense with esoteric learning, and turns on a pattern that becomes clear only too late. It influenced everyone from Umberto Eco to the writers of True Detective. Reading it is like watching a beautiful, fatal geometry unfold.