Beth Chambers 
Dicing with Death [EPUB ebook] 

Max used to be an ordinary boy… until he offered himself up to Death in the place of his little sister, and somehow ended up as Death”s assistant! Life in the Underworld isn”t all bad though, despite housekeeper Liah”s abysmal cooking.
Above ground, someone has worked out how to bring the dead back to life, with potentially universe-destroying consequences. Can Max and Liah stop the culprit in time? Or will Max get a lot more than he bargained for?
A darkly comic fantasy adventure in the Black Cats series: short, gripping stories for newly confident readers aged 8-12.