A mysterious arrival at Kirrin Cottage, in the middle of the night, sparks excitement amongst George and her cousins. Berta is a vulnerable, young American girl, (daughter of a rich man) who is fleeing kidnappers and the Kirrin Household have been personally asked to protect and disguise her. In order to make her unrecognisable, Berta is transformed into a handsome looking young boy called Lesley – and the Five are constantly on the look out for potential kidnappers. Will the disguise be successful, or will Berta be recognised and therefore find herself in grave danger?