'Come back, George - there may be danger!' shouted Julian, but George didn't listen.
This summer the Five will become six - and George isn't happy about it. American girl Berta has been threatened with kidnap, and Kirrin Cottage is the only place she can hide.
But Berta's arrival puts them all in danger when someone starts spying on them from Kirrin Island. Berta may be in disguise, but can they keep her safe and protect her from the kidnappers?
This softback book written by Enid Blyton with inside illustrations by Eileen Soper was originally published in Great Britain in 1955. This edition was published in 2016.