The Unmapped Chronicles is set in the Unmapped Kingdoms, which exist alongside our continents, holding all the magic needed to fill the earth with wonders and stir the senses of humankind. But with the appearance of an evil harpy, Morg, the people of the Unmapped Kingdoms must reach out for help if they are to survive.
Griffiths said: "Abi has already established herself as one of the best authors writing middle-grade fiction today, and I couldn't be more thrilled to have signed up three new books. Sitting firmly in her heartland of adventure, magic and wonder, The Unmapped Chronicles is something very special and will catapult Abi to even greater heights!"
Elphinstone said: "The trouble with inventing stories is that they have a habit of growing at alarming speeds. The idea for this new series started small - a phoenix egg, seven magical tears and a handful of golden feathers - but before long I had castles built on the backs of sleeping Cloud Giants, underwater cathedrals and talking dhow boats, a triplet of Drizzle Hags (hello Hortensia Quibble, Sylvara Buckweed and Gertie Swamp) and a Storm Ogre who can only say one word: 'chomp'. I suppose that's the curse of working in a career that dabbles with the imagination; things just get hopelessly out of control."
Abi's previous books are:
She also edited and collated the Winter Magic anthology. Sky Song was recently selected as Waterstones January Children's Book of the Month.
Follow Abi on Twitter: @moontrug