When the young and lovely Violet Smith arrives to consult with Sherlock Holmes, he first regards the experiences related by her with a degree of impatience and disinterest. He's busy on another matter you see, but there might be something in her story.

She enjoys cycling and tells about being shadowed by a mysterious man on a bicycle as she cycles to and from her new employer's home as a music teacher. As Holmes and Watson investigate, a dark, dangerous picture begins to emerge that threatens the young lady's safety and ultimately her freedom. Holmes takes up the case.