Five on a Secret Trail by Enid Blyton
FIVE ON A SECRET TRAIL - The Famous Five are camping near an old ruined cottage - but is the cottage really abandoned Anne hears strange noises at night - but the others don't believe her! Then they see the ghostly light . . .FIVE GO TO BILLYCOCK HILL - The Famous Five have made a new friend - a pilot! But he has disappeared with top secret equipment. The Five can't believe it - is Jeff a traitor