Belle of the Ball — Anne Holman

When merchandise is stolen from the shop where Isabel Hindley works, she and the other shop assistants are under suspicion. So when Lady Yettington is observed going out of the shop without paying for goods, Isabel accuses her ladyship of theft, making her nephew, Charles Yettington, furious. But things are more complicated when Lady Yettington is put under surveillance, and more merchandise goes missing. Isabel and Charles plan to find out who is responsible.