It is difficult for Martin to convince the people of St. Hubert to allow him to run his experiment as opposed to simply giving everyone the phage. Inchscape and Governor Fairlamb are both against it, and so Martin has to have the matter taken up by a board that consists of Inchcape, Fairlamb, the Board of Health, members of the House of Assembly, and Sondelius himself. Everyone is against Martin's experiment, except Dr. Stokes and Dr. Oliver Marchand.
There is an incident at the Board meeting where Ira Hinkley stands and speaks poorly of Martin, calling back his experiences of having been suspended from Winnemac and further criticizing Gottlieb's incompetence. Sondelius stands up for Martin and Gottlieb to the point where Hinkley is asked to leave and the board decides to consider the experiment. Sondelius says he will stand by Martin. However, he still refuses to take the phage himself.
After the Board meeting, a man named Cecil Twyford, of St. Swithin's Parish confronts martin and tells him he is sorry about how the board had reacted to his request and that he could do something in St. Swithin. Four days later, Ira Hinkley dies.
Martin returns, then, to the village of Carib, where he had visited earlier, and which is in utter despair. He gives the phage to the entire village. The plague decreases but, because of the infected ground squirrels, both Martin and Sondelius believe that the village has to be burned in order to be completely disinfected. Both men then proceed to evacuate the villagers and place them into a temporary tent, after which they burn the village. It is at this point that Sondelius catches the plague and dies. Sondelius's dying words to Martin are to please give all of the people the phage. Martin, however, will not sway.
Back in Blackwater, Martin is despised by the people - they call him names and throw stones because they believe he is withholding their salvation. Inchscape falls to pieces and deserts the island, after which he commits suicide. It is at this point that Stokes is appointed Surgeon General and Martin is finally allowed to conduct his experiment because of an agreement worked out by Stokes and Cecil Twyford. Martin will conduct his experiment in St. Swithin.
Martin leaves St. Hubert for St. Swithin, leaving Leora behind for fear that it will not be safe for her and promising to send for her if he sees that it is alright. Once in St. Swithin, however, Martin meets a widower named Joyce Lanyon, a rich New Yorker who had gone to St. Hubert to check on her plantations and had become caught in the quarantine. Martin is attracted to her and feels tempted as he had with Orchid.