Among the most accomplished features by director Jean-Devaivre (whose career helped inspire Bertrand Tavernier’s SAFE CONDUCT), this thriller puts the conventions of the detective film to wonderfully entertaining use. When a pharmaceutical magnate begins receiving anonymous threatening letters, Stanislas-Octave Seminario (future DIABOLIQUE star Paul Meurisse) is enlisted to help; as “SOS” investigates, the mystery deepens when a member of the magnate’s family is poisoned, murmuring “the lady of eleven o'clock” as he died.