The series numbering is wrongly printed on the title page as volume 5.
"This book is one of twenty which comprise the complete, detailed manuscript which the author prepared for the Blue guide: Greece, the Aegean Islands (2010), and on which the Blue guide was based. Some of this text therefore appears in the Blue guide" -- t.p. verso.
OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
Rhodes with Symi & Chalki by Nigel McGilchrist. ISBN 9781907859052. Published by Genius Loci in 2010. Publication and catalogue information, links to buy online and reader comments.
