Angel of vengeance

"A desperate bargain is broken ... 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. A clever trap is set ... 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 Fi...