London 1924. While investigating the theft of a priceless necklace, Lady Eleanor Bakewell spends an evening at the theatre, but her enjoyment is curtailed by the discovery of the body of Sir David Bristol, the play's benefactor, in the box next to her own.
Determined not to get involved, Eleanor is reluctantly forced to look into the case following requests by the murdered man's mistress and a major in Military Intelligence.
When she discovers a connection between the string of pearls and the murder, Eleanor is faced with her hardest case yet, and a gang of spies who will stop at nothing to silence her.