London, 1870: A Hungarian immigrant is found dead in what appears to be a ritualistic killing, with a bayonet through his heart, his fingers broken and his body surrounded by seventeen blood-dipped candles. At first, Commander William Monk of the Thames River Police suspects the killer is from within the victim's community; but when another murder takes place, Monk fears the immigrants are being targeted by an outsider. Meanwhile, Hester is reunited with a doctor who had been left for dead on a Crimean battlefield. Traumatised by his experiences, Fitz has made his way home via Hungary, and is now living in the immigrant community. Hester is determined to help him - and when he is accused of the killings, she sets out to prove his innocence...