Lynn Morley, a girl with quite an imagination, believes that her older sister, Judith, is being trained as a witch by their neighbor, Mrs. Tuggle. No one else seems to notice Judith's strange new behaviors and habits, like reading tarot cards and spending time with a mysterious young man whom she raised from the lake near their house. Convinced that she alone must stop her sister from falling completely under Mrs. Tuggle's influence, she and her best friend Mouse attempt to gather evidence. Just as Lynn realizes her young brother may be in danger, their mother is called away unexpectedly and Lynn and her siblings are left in Mrs. Tuggle's care. Will Lynn be able to break the spell before her little brother becomes Judith's victim? This film was originally broadcast in chapters during several episodes of the television show BIG BLUE MARBLE. It was later shown on cable networks as a movie.