In 1910 New York City, four years after her father dies of tuberculosis, ten-year-old Essie's fear and anxiety continue to grow uncontrollably, so much that when her mother, a brave nurse, remarries and the family moves to North Brother Island, where Essie's new stepfather runs a quarantine hospital for the incurably sick, Essie imagines all manner of horrors, including the ghost of a little girl--which might not be imaginary after all.