Diane Bradley 
Wilder’s Foe [EPUB ebook] 

Mysterious lights are appearing on Rainy Lake. When Henry, Dylan, Arla, and Rika hear that ghosts are visiting the lake, they laugh it off. But as they kayak back over the route where Arla’s parents disappeared ten years before, they find themselves stranded on an island, haunted by a real ghost, who doesn’t want them to leave . . . ever.