Brian Innes had been asked to see young Audrey Page when she arrived in Geneva and to detain her from joining the strangely temperamental group of people at the Villa Rosalind. With characteristic stubbornness, if not trusting naiveté, she goes and is immediately encircled by terror, while the jaws of a murder trap swing closed. Fortunately, Dr. Gideon Fell is on hand, and when the muderer strikes with an invisible weapon, Fell accepts the challenge with brilliance and wit.