The Parable of the Knocker is a nonfiction book about the investigation, prosecution, and trial of a notorious serial killer, Charles Severance. Severance committed his crimes in the City of Alexandria, Virginia, an affluent, historic community just miles south of Washington, D.C.

Over the course of a decade, Severance ambushed three outstanding Alexandria residents in their middle-class neighborhood by knocking on their front doors in broad daylight and shooting them unexpectedly when they answered the knock. Severance was not personally acquainted with any of his victims, and instead selected his targets to revenge perceived wrongs and terrorize a community.