When Lord Palfrey, from whom Eleanor hopes a substantial donation, arrives for a guided tour of the Thrift, every patient in sight seems to be practicing projectile vomiting. Eleanor thinks it's food poisoning, but Robert diagnoses cholera. Eleanor is forced to notify Dr. O'Neill (who is the designated Medical Officer), who calls in the public-health inspector. The source of the infection is quickly determined to be an unsanitary condition in the immigrant colony at Jacob's Island, but the ill patients must still be treated.Dr. O'Neill, as it happens, is the leading authority on cholera, and has developed a pioneering though as yet unproven cure (called, somewhat unpromisingly, Compound 108). Eleanor authorises O'Neill to administer his treatment, though Robert is not convinced that it is safe.Two twin children are both doing well when one suddenly dies. Robert discovers she was given 12 grams of O'Neill's cure, which contains an arsenic compound, whereas the other was given only 4 gra (thetvdb.com)