Lord and Ladies by Terry Pratchett

The fairies are back – but this time they don’t just want your teeth. It’s Midsummer Night – no time for dreaming. Because sometimes, when there’s more than one reality at play, too much dreaming can make the walls between them come tumbling down. Unfortunately there’s usually a damned good reason for there being walls between them in the first place – to keep things out. Things who want to make mischief and play havoc with the natural order.

Granny Weatherwax and her tiny coven are up against real elves. And even in a world of dwarfs, wizards, trolls, Morris dancers and the odd orang-utan, this is going to cause real trouble. With lots of hey-nonny-nonny and blood all over the place.