Sherlock pursues Howard Ennis, an unpredictable criminal, before he strikes again. During the investigation, Sherlock is forced to work alongside Kathryn Drummond, the FBI profiler who literally wrote the book on Ennis. Meanwhile, Watson faces eviction from her apartment.

Sherlock investigates what he believes will be an open-and-shut case after Detective Bell is attacked. However, the case takes an unexpected turn when the suspected assailant is found dead. Meanwhile, Sherlock encourages Joan to learn self-defense.