The essay shall strive to emphasize the significance—harmonic, structural, and metaphysical—of what might readily be considered one of the most remarkable harmonic procedures in Mozart. It appears in middle of Don Giovanni’s Sextet “Mille torbidi pensieri”. Here, we find the sudden and dramatic imposition of the parallel flatted seventh chord of the tonic, one of the composer’s more revelatory episodes. The spiritual associations of this descending, quasi-modal, parallel-motion-chord in this most unusual progression will be referenced through further manifestations in Mozart’s own work and compared with other, antecedent composers—most notably Bach—to reveal what I believe is a distinct aspect of the flat-seven harmony in the music of the eighteenth century.