On his return to Geneva, Brian Innes must meet Audrey Page and find a way to prevent her from joining the strangely temperamental group of people gathered around film star Eve Eden at the Villa Rosalind. With characteristic stubbornness, if not trusting naivety, she refuses to be detained 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 murderer strikes with an invisible weapon, Fell accepts the challenge with brilliance and wit.