12 year old Harmony Parker is obsessed with animals. She and her best friend Tom have set up an amateur vetinary practice in a small tent in her back garden yet her parents won't allow her to have a pet. However, hopes of a pet are in sight when Harmony's eccentric and mysterious Uncle Ginger pays her family a brief visit and leaves her with a deceptively normal looking 50 pence piece. Harmony soon discovers that the coin posseses wish granting powers and learns through the course of the series to be careful what she wishes for.