Rob Lloyd Jones 
Wild Boy and the Black Terror [PDF ebook] 

The second in a series of pacy mystery-adventure stories for 9+ readers, set in the seamy, smoggy underworld of Victorian London.A new sensation grips London – a poisoner who strikes without a trace, leaving victims mad with terror … and then dead. Is there a cure for the BLACK TERROR? To find out, Wild Boy and Clarissa must catch the killer. Their hunt will lead them from the city’s vilest slums to its grandest palaces, and to a darkness at the heart of its very highest society.