Fahrenheit 666 by Andrew Harman

Everybody needs a holiday, and demons are no exception. There may be an important election going on in the hellish city of Mortropolis, but most minds are on forthcoming breaks -- maybe possession of a teenage nymphomaniac for a fortnight, or canoeing down the Styx with a packed lunch...

But life in and around Cranachan was no picnic. Well, what with mad desert tribesmen ram-raiding their farms, a series of mysterious murders, and the temperature hotting up it was almost as if Hell was about to break loose -- literally!

Fahrenheit 666 is Andrew Harman's fifth bestselling humorous fantasy.