Six-year-old Ethan and ten-year-old Bea are confused. Grandma looks sad, hurts all the time, has dark circles under her eyes, can't toss a ball or frisbee, and doesn't take care of herself as she did in the past. Ethan mistakes a shooting star for a UFO and convinces Bea Grandma has been possessed by an alien. Adults call it arthritis. Is that to prevent people from being scared because it's catching? They hatch a plan to prevent the alien from taking over Mom, too.