The Masquerades of Spring : The Brand New Rivers of London Novella by Ben Aaronovitch

Meet Augustus Berrycloth-Young - flaneur extraordinaire and Englishman abroad - as he chronicles the Jazz Age from his perch atop the city that never sleeps.

'Gussie' is not one to shun shut-eye himself, however. But his peaceful luxuriation is about to be rudely awakened by the arrival of an unexpected guest.

Enter his old friend Thomas Nightingale, who has braved the Atlantic passage pursuing the matter of a rather intriguing saxophone said to possess a strange power over those who play it. This deeply inconvenient affair will rouse Gussie from his warm bed for the cold shores of Long Island - and down to the jazz clubs of Harlem where music, magic, and madness haunt the shadows...