Cryptic Casebook of Coco Carlomagno (and Alberta): Quivering Quavers -- Paperback

La Bella Cucharita, the highly strung world-famous opera singer, is due to make her return to the stage after an unfortunate nerve-wracking incident - but a strange message has her rattled. Who on earth would send La Bella Cucharita mysterious notes on the eve of such an eagerly awaited performance?