The Secret Mark (Unabridged)

Student Lucile Tucker works part-time at the library of the large university she attends in Chicago to help pay her tuition. One night, while closing the library for the evening, she glimpses a small child - a girl - in the stacks. Carefully following her, Lucile can't believe her eyes when the child, unaware that she has been seen, manages to steal a valuable book from the collection and practically disappear from the library right before Lucile's eyes.
This is only the beginning of her search for why this child took this book . Lucile enlists the assistance of her good friend and roommate Florence, a fellow student, to attempt to solve this mystery on her own. She can't bear the thought of this sweet-faced child being turned over to the police despite her apparent thefts. Enter the world of these college women as they brave the city streets at night in unsavory sections of Chicago on their quest.
Who is the elderly man in the crumbling cottage? What is the significance of the 'mark' inside the front covers of the books? Has someone been shadowing the women on their search. Listeners outside the USA: Roy J. Snell died in 1959. The author's work is still protected by copyright in places, like Europe, where copyright is author's death plus 70 years, and Australia .