Seventeen-year-old Cassie Brittman is looking forward to her violin recital and the prom-and then the hospital calls. Her grandfather, noted painter Daniel Brittman, is dying. Cassie, her mother, Anne, and Anne's new boyfriend drive upstate to the farm where Anne was raised-and find that things are far from normal. The house is almost destroyed, except for Great-Grandmother Hannah's herb garden, and someone (or something) seems to be stalking them. Cassie soon finds herself at the center of an age-long battle between two supernatural clans-the sinister Red Clan and her own family, the Green Clan. For it turns out that Cassie's grandfather is half nature spirit, half human. . . .