A short distance away from Ardencraig Point where Nick and Peter were camping lay the island, tantilisingly near yet too far to reach without a boat. Yet it was upon the island and its secret that the adventure centred - the adventure which began with the astonishing discovery the boys made while exploring the old lead-mines and a chance-recalled remark their history master had once made. Or perhaps it was the mysterious flickering lights on the roof of Ardencraig Castle that really started it all.