While out fishing one bright summer day, fifteen-year-old Tommy Oakley is startled to spy what appears to be a giant fish surfacing in the inlet near Mulberry Island. Confused and a little fearful, he returns to Bayside, the tiny village where he lives, and recruits Wendy to help him solve the mystery.
A few nights later, Tommy goes camping with his best friend John, and they’re alarmed to see ghostly lights floating above the water and movement inside the island’s abandoned mansion.
Everyone in Bayside knows the island is uninhibited, but they also think it’s haunted, so Tommy and John are more than ready to stay away. But the strong-willed Wendy convinces the reluctant boys to investigate the source of the lights, thereby setting in motion a harrowing adventure that has them dodging bullets and running for their lives, all the while struggling to sort out their conflicted feelings for one another.
One thing is certain—if they survive the summer at all, things will never be the same between them again.