Carroll Baker delivers a captivating dual performance as Julie Harrison, a translator, and her twin sister, Mary. The intricate story unfolds with Julie confiding in her lawyer, Dave Barton, about the looming danger threatening Mary in London. Meanwhile, a shadowy figure is pursuing Julie in Amsterdam, adding to the tension. As the narrative twists and turns, both sisters find themselves entangled in a web of intrigue and peril, highlighting themes of danger and deception that keep viewers on the edge of their seats.