The title comes from Revelations 6:8, which in the King James Version says, "And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him."
Hook is that each section starts with "His name was" or "Her name was." The book begins, "Her name was Joyce Dugan, and at four o'clock on this February afternoon she had no remote thought that within the hour before closing time she was about to commit an act that would instigate a chain of murders." The last section, just a couple of pages long, begins, "His name was Death, and he waited for """"."
After Dugan, the focus moves around a few other people, primarily her boss, Darius Conn, who runs a print shop. The year before he'd killed his wife and gotten away with it, and now he's feeling bold and very confident. He's got a plan, and no-one's going to get in his way.