In Chapter 18 of Bram Stoker's "Dracula," the pistol shot is fired by Quincey Morris. His motivation is to stop the Count (Dracula) from escaping after the group of characters, including Jonathan Harker, Mina Harker, Professor Van Helsing, and others, confront Dracula at his castle. Quincey Morris sacrifices himself in this act, as he delivers a fatal gunshot to Dracula. Morris's motivation is rooted in his commitment to protect Mina and eliminate the threat posed by Dracula.