Mary Quinn, a young woman alone in Victorian London, is about to hang for thievery when she is whisked away and offered a new life in a women’s academy. Eventually she learns the academy is a front for an all-female detective agency. Mary’s first assignment takes her to the home of a wealthy merchant, where she is to gather evidence of wrongdoing while posing as a companion for his daughter. It is soon apparent that his household has more than its share of secrets. Mary finds herself forced to partner with James, the brother of her young charge’s suitor, who has suspicions about the family. The first in a series, this volume sets up its premise in an unobtrusive manner. There is interesting chemistry between Mary and James as well as hints that they may reunite in a future volume. The descriptions of a crowded, smelly and unsanitary city are both well-drawn and important plot elements, as are the mores of Victorian life. Most intriguing is the unusual ethnic heritage Mary strives to conceal, which adds a fresh dimension. (Historical mystery. 12 & up)