Checkmate
 The innocent girl is 24 year-old Mary Mallory, who has spent the last seven years in isolation caring for her invalid aunt. After the latter's death, Mary, now living in London, realizes that she has to earn her own money unless she wants to live in relative poverty. She answers the ad of a Comtesse Zamoyski, who is looking for a companion with whom to travel to the Côte d'Azur, and, after an interview, she is accepted for the post. As Mary sees it, her new job combines at least two advantages: seeing the world and proving, to herself as well as her friends, that she is an independent woman. Mary's blinkered view lets her ignore all the warning signs that are pointed out to her. Jessie Stevens, her old schoolmate, even suspects that "White Slavery" could be behind that ad, but Mary does not listen and leaves London with her new employer. Through a series of coincidences a number of people are alerted to the dangers that might be in store for Mary. Apart from Jessie Stevens, it is Dick Delabrae, a society columnist for The Sun, and his friend Robert Wingate, who happens to be the nephew of Lady Wentworth, whose pearls the gang wants to steal. They all come to Cannes, where the Comtesse Zamoyski and Mary Mallory are staying in a remote villa, in order to help the young woman and prevent the theft of the pearls. The Comtesse turns out to be rather moody, but at first Mary has no idea that she is associating with criminals. Her first visit to the Casino is a huge success: Not only does she win more than ₤1,500 at baccarat but she also makes the acquaintance of Lady Wentworth, who immediately takes a liking to the charming girl. Later that night, however, back at the villa, she overhears a conversation between the Comtesse, José Santes, allegedly the Comtesse's nephew, and a young Russian called Nadja, allegedly her maid, which makes it unmistakably clear to her that she is staying under the same roof with criminals. However, escape is now no longer possible. Before she can get away from the villa, Mary Mallory is captured, drugged and hypnotized by the fourth member of the gang, a Frenchman posing as a doctor. On his way to the villa to rescue Mary, Robert Wingate, who has fallen in love with Mary, is kidnapped by Santes's men and thrown into catacombs somewhere below the streets of Cannes. Lady Wentworth is lured to the Comtesse's villa with the prospect of seeing Mary again but after her arrival she is tied to a chair and, in a drug-induced frenzy, stabbed to death by José Santes, a "dope fiend". As she is not wearing her pearls, the gang flee without any loot. When Mary Mallory wakes from her stupor some time later it is only to encounter the French police accusing her of murdering Lady Wentworth, whose body she discovers in the same room where she was lying unconscious. But Robert Wingate can escape from the dungeon, and all misunderstandings are cleared up in the end. The members of the gang are arrested near the Italian border, and the two couples &mdash; Dick and Jessie on the one hand, Robert and Mary on the other &mdash; return to England to get married.