Famous Five - Book 15: Five On A Secret Trail

Camping again! This time the Five have pitched their tent near an old ruined cottage, which looks as though it's been abandoned for years. When Anne hears strange noises at night the others don't believe her...until they see ghostly lights. Could the cottage be haunted?

The Five are camping out on the common, near an old, empty cottage where strangers keep nosing around in the dead of night, looking under stone slabs of a certain size. Why all the secrecy? Why do the strangers put on a ghostly light show to scare the Five away?