When the Five go to spend their holidays at Tremannon Farm on the Cornish Coast, they learn about the location's incredible past concerning some evil examples of smuggling. The peacefulness and tranquillity of the area now suggests that these days are well and truly gone, but then one stormy night, the lights appear again, and Tremannon's dreadful past comes flooding back.
 
The Famous Five sense danger. But can they solve this mystery without getting hurt themselves?