Enola Holmes receives a secret message hidden in a pink fan from her friend Lady Cecily, who is in danger. Enola discovers that Cecily has been kidnapped and taken to a strict institution where she is being forced into an unwanted marriage.
Using her skills in disguise and investigation, Enola searches through London to find her friend and uncover the truth. The case becomes more complicated as she must avoid being caught by her brothers, especially Sherlock and Mycroft.
In the end, Enola manages to rescue Cecily and stop the forced marriage, while also continuing to build her identity as an independent young detective.