The plucky Fitzgerald-Trout siblings (who live on a tropical island where the grown-ups are useless but the kids can drive) are back! After losing the boat that had become their home, oldest Fitzgerald-Trout, Kim, has put finding a home back on her to-do list. When her sixth-grade history assignment offers a clue about the ruins of a volcanic house built by an explorer on Mount Muldoon, she and her siblings set out to find it.
The castle they discover surpasses their wildest dreams. But having a permanent home offers more challenges than the Fitzgerald-Trouts expect, especially when they begin to suspect their home is haunted. The siblings must figure out how to fix the cracks in their family foundation before one of them is lost for good.