FBI Special Agent Aloysius X.L. Pendergast and Sergeant Vincent D'Agosta, now working for the Southampton Police Department, investigate a series of unusual deaths—deaths that appear to be the work of Lucifer in return for pacts entered in with him by his victims.[2] Their investigation takes them from the New York City area, site of the first two deaths, to Florence, Italy where they uncover the motive and method of the killers behind the strange and gruesome deaths. During the course of unraveling the mystery, the truth behind a priceless, missing Stradivarius violin is revealed and a potentially apocalyptic riot with Messianic Christians is averted. Pendergast also reveals details of his insane brother Diogenes, whom he believes is planning something horrible.