The Quintessence of August

During an August heat-wave, the Comte de Saint-Germain seeks the help of detective Auguste Dupin. Someone - or someTHING - is trying to kill him! The Comte has inherited a magical cello and a mysterious sealed box. A psychic vampire (an "egregore") intends to use the cello and a magical musical composition to steal another soul. Can Dupin and his faithful companion unravel the puzzle in time to save the Comte?