Janey Wiggins lives a desperate life in London's East End at the end of the nineteenth century. With little education and fewer prospects, she has no hope of escaping the grinding poverty, constant hunger, and ever-present danger of life on the street -- that is, until a chance meeting with the great detective Sherlock Holmes and his friend Dr. Watson. Hired on as Holmes's apprentice "irregular," Janey turns her adversity to her advantage. As she and her friends investigate the mysterious appearance of a ghost in the upper window of a local home, Janey discovers how important she can be. But when her theory of the case clashes with Holmes's and a child's life may be on the line, will she find the courage to act?