Murder, spies, mathematics and music - it's all in a day's work for Phryne Fisher in her 20th adventure!An orchestral conductor has been found dead and Detective Inspector Jack Robinson needs the delightfully incisive and sophisticated Miss Fisher's assistance to enter a world in which he is at sea. Hugh Tregennis, not much liked by anyone, has been murdered in a most flamboyant mode by a killer with a point to prove. But how many killers is Phryne really stalking?At the same time, the dark curls, disdainful air and the lavender eyes of mathematician and code-breaker Rupert Sheffield are taking Melbourne by storm. They've certainly taken the heart of Phryne's old friend from the trenches of WW1, John Wilson. Phryne recognises Sheffield as a man who attracts danger and is determined to protect John from harm.With Mendelssohn's 'Elijah', memories of the Great War, and the science of deduction ringing her head, Phryne's past must also play it's part as MI6 becomes involved in the tangled web of murders.