Jane Cleveland, a young woman of twenty-six is in need of a job. Her financial position is precarious and she lives in a shabby boarding house. Browsing the Daily Leader jobs column she finds nothing of note but in the personal column she sees an advert for a young woman of her age, build and height who is a good mimic and can speak French. She goes to the address given and is one of many girls queuing up in answer to the advert. Getting through to the final six, she is interviewed by a foreign gentleman and told to go to Harridge's hotel and ask for Count Streptitch. Presenting herself there as instructed, Jane is again interviewed by the Count and then introduced to an ugly middle-aged lady by the title of Princess Poporensky who both declare her to be suitable. They ask Jane if she doesn't mind the prospect of danger to which she answers that she doesn't. Finally, Jane is introduced to the Grand Duchess Pauline of Ostrava, exiled from her country after a communist revolution. Jane is similar in looks and colouring to the Grand Duchess although she is slightly smaller in height. It is explained to Jane that the Grand Duchess is the target of assassination attempts by the people who overthrew and slaughtered her family and that they want Jane to act as a decoy for her during the next two weeks when she is in Britain and has to attend several charitable events. Jane agrees and is given money to stay at the nearby Blitz Hotel (under the assumed name of Miss Montresor of New York) and to buy a dress to wear when she is following the Grand Duchess to the events, during which they will swap dresses when they suspect that a kidnap or murder attempt is imminent. Jane suggests a bright red dress in contrast to the Grand Duchess' dress of choice for a charity bazaar at Orion House ten miles outside of London and that she will wear high-healed boots to cover up the difference in height.
Three days later, the bazaar is taking place. The main feature of it is that one hundred society women will each donate one pearl each, which will be auctioned the next day. The real Grand Duchess declares the bazaar open and meets the people there. When it is time to depart, she and Jane swap dresses in a side room and Jane leaves in the Duchess' place – news having reached them that the assassins will make an attempt on the journey back to Harridge's. Jane is travelling back with the Princess Poporensky when the chauffeur takes them down a side road and down an unknown and secluded route, stops the car and holds up the two women with a pistol. They are at an empty house, which they are locked in. A short time later, bowls of soup are given to the two women, which Jane eats but the Princess refuses. Jane falls asleep suddenly...
The next day Jane wakes up. She is alone in the house and inexplicably back in her red dress. She finds a newspaper in the house, which states that the charity bazaar was help up by a girl in a red dress and three other men. They stole the pearls and got away. The girl in the red dress has been traced as staying at the Blitz Hotel under the name of Miss Montresor of New York – Jane realizes that she has been set up by a gang of jewel thieves. She hears someone in garden and finds a young man coming round from having been knocked out. He and Jane swap stories and the young man reveals that he was at the bazaar and was puzzled when he saw the Grand Duchess enter a room in low-healed shoes and exit in high-healed ones. He followed her to the empty house and saw a second car arrive with three men and a woman in a red dress. Presently, this woman came out in the Duchess' dress and all except Jane seemed to have departed but when the young man went to investigate he was knocked out. They suddenly become aware that another man is nearby and listening to them. He introduces himself as Detective-Inspector Farrell and having overheard the stories that the two told all has become clear to him and he realizes what really happened at the bazaar hold-up and that Jane is innocent. The young man reveals that having seen Jane at the bazaar, he has fallen in love with her…