Actress Helen Johnson, recently married to an officer in British Intelligence with whom she once worked, feels she lacks the nerve to join him in a further life-and-death assignment such as that she undertook in Whoever I Am, described by The Times as 'in the Christie thriller manner'. Nevertheless, she still wants to exercise her unusual talents. It is after light-heartedly offering 'a unique service' through the advertisement columns of some magazines that she finds herself playing three such diverse parts as the bridegroom's only relative at a suburban wedding, the girlfriend paraded for the approval of Mama, and the wife of a would-be business executive who must be assessed along with her husband -- not on the stage but in real life. She also finds herself innocently in trouble on a scale to send her back after all, and without choice, into another role where not only is her life at stake but her husband's life also and the safety of their home. In the psychiatric clinic where Helen must anonymously go both to hide and to seek, can it really be that someone is trying to poison her?
Can an internationally sinister development really be taking place alongside the innocent life of the hospital? This is horror enough, but it is when a very special patient is admitted that Helen's ordeal turns to nightmare and she is force to use her talents, her courage and a desperate ruthlessness in an effort to protect all she holds dear. As in her earlier adventure, 'the incidental realities are as terrifying as the plot' (Listener).