After a summer of tagging sharks off the west coast of Florida, Sabina, Maribel, and Luke have a new assignment: searching for "survivor trees" that are resistant to the disease that is destroying the state's citrus trees; the search takes them to the remote mangrove islands of Sanibel Island, where they discover Spanish oranges, a grave, an immense saltwater crocodile, a reclusive woman who believes that the ghost of a dead king, beheaded by Spanish explorers, is haunting her, and her neighbor who is involved in the illegal reptile trade--and in their effort to protect the woman and her animals they are soon plunged into a struggle for survival.