A string of bizarre and horrific murders are taking place in and around a travelling English circus. Wherever it goes, someone dies.
During one of the daredevil performances, a knife is thrown into the back of high-wire walker, Frank (Ty Hardin). He dies, falling onto the sharp spikes below, to the horror of the big top audience, other circus performers, and Monica (Joan Crawford). Monica is the circus owner and ringmistress.
Monica's daughter, Angela (Judy Geeson), then reveals herself as the killer and confronts her mom. Angela's father/Monica's husband died years earlier, and Monica tried to fill the void of her husband's absence by placing other people in her life, and in the process would ignore Angela. After years of this emotional abuse, it became too much for Angela to bear, and she finally went crazy and just needed to kill, kill, kill anyone taking her mom's time!
As Angela is about to lunge a knife at her mother, the constables that were on hand try to stop her. Angela runs outside the circus big tent, just as a lightning strike hits an electrical pole that causes an electrical line to fall to the ground, electrocuting her.