Constance Greene confronts Manhattan’s most dangerous serial killer, Enoch Leng, bartering for her sister's life. But she is betrayed and turned away empty-handed, incandescent with rage. Unknown to Leng, Pendergast’s brother, Diogenes, appears unexpectedly, offering to help --- for mysterious reasons of his own. Disguised as a cleric, Diogenes establishes himself in New York's notorious Five Points slum, manipulating events like a chess master, watching Leng’s every move…and awaiting his own chance to strike. Meanwhile, as Pendergast focuses on saving the unstable Constance in her fanatical quest for vengeance, she strikes out on her own: to rescue her beloved siblings from a tragic fate and take savage retribution on Leng. But Leng is one step ahead and has a surprise for them all.