The wonderful chance came along in 2006 to write Faeries of the Celtic Lands, a book I've been wanting to do for over half my life, thanks to my publisher Cameron Brown who simply asked over lunch in the Chelsea Arts Club in London what I would most like to write about.

Celtic mythology has long been one of my obsessions and although I've squeezed snippets of it into many books, the only previous chance I had to concentrate on it to any great extent was in the 1999 book on Leprechauns I wrote for Wayne Anderson to illustrate. So this was a complete delight, even if it did mean that for months I was barely able to hold a sensible conversation about anything else with friends and family, let alone work colleagues. But, it still felt worthwhile because doing this book justice mattered more than anything else.

The aim of the book is to trace the origins of the Celtic beliefs about faeries back to the misty days of their first arrival in Ireland, apparently descending from the sky in flying ships and landing on the mountain tops amid a great cloud that shrouded the land for three days. According to legend they then ruled the country as gods for an age before being forced to retreat into a parallel world, or sail away westwards across the ocean like Tolkien's elves. From the earliest Irish records the tale is then taken up in the legends of the other Celtic lands - Wales, Scotland, Brittany and Cornwall.

The book is due to be published on 1 November and is a fair bit longer than most I've had published so far, in proportion to my interest in the topic, though without anywhere near exhausting it. The idea is to give a kind of overview of the subject for those who are curious and even quite well informed about Celtic mythology, but daunted by its abundance and seeming chaos. Also to examine how the basically pagan ideas in the faerie faith nevertheless managed to survive and prosper alongside Christianity right up to about a century ago when other forces undermined the solid belief in faeries in the Celtic countryside.