Grace Marks
Grace Marks is at the center of an intriguing mystery. Did she kill her employers in cold blood or was she an unwilling accomplice? She claims she cannot remember the actual murders, having blacked out, but witnesses, including Jamie Walsh, testified she did things she now cannot recall. Her lawyer thinks she's "guilty as sin," her doctor at the asylum thinks she is a "cunning liar," and the newspapers paint her as a seductress. She was spared the death penalty due to her young age and the general belief that women are less capable of murder than men. Thanks to her exemplary behavior in prison and her generally pleasing manner, she has gained an influential following of people who think she is innocent. Telling her story to Dr. Simon Jordan, Grace paints herself in a sympathetic light, casting significant doubts on her own complicity. She plants hints that she is somehow possessed, either literally or figuratively, by her dead friend Mary Whitney. During her hypnotism, the normally chaste Grace erupts in coarse language and claims to be Mary. "Mary" admits to the murders. The experts are perplexed. Does this secondary personality absolve Grace of guilt? Or is she merely playacting to secure her own pardon? Though she waits many years, Grace is finally released and marries Jamie Walsh. Her ultimate guilt or innocence remains unclear. However, as in the lyrics of the hymn "Amazing Grace," Grace has finally been seen clearly.
Dr. Simon Jordan
Dr. Simon Jordan is named after the apostle Simon Peter, whom the Bible says was a fisher of men. After his extensive interviews with Grace, he confesses that "like [his] namesake" he has cast his nets, but he fears that he has only drawn up a dangerous siren. As an ambitious man, Dr. Jordan sees Grace as a way to make a name for himself in his field if he can only "cure" her amnesia. Reverend Verringer has hired him to prove Grace's innocence. However, Dr. Jordan finds Grace "a hard nut to crack," and he does not make much progress until he agrees to a hypnotism session. In that session, the skeptical Dr. Jordan is shocked when "Mary" appears and takes the blame for the murders. Dr. Jordan understands that reporting on what he saw would ruin his career, so he must leave without ever discovering the truth. It is bitterly ironic that Dr. Jordan ends up suffering the same type of amnesia that he suspected of Grace.
Nancy Montgomery
Grace accepts a position with Nancy Montgomery because she believes Nancy could be her friend, as Mary Whitney was. However, Nancy turns out to be jealous and two-faced. She is sweet and friendly when Mr. Thomas Kinnear is not around and stern and annoyed when he is. Grace finds Nancy difficult to please owing to her changeable nature. She also feels betrayed by Nancy when she discovers Nancy is sleeping with their boss. Nancy and James McDermott hate each other, so Nancy is not surprised when Grace tries to warn her that McDermott will try to kill her. Nancy suffers an axe wound and strangulation. After her death, she is found to have been pregnant, most likely with Mr. Kinnear's child.
Mr. Thomas Kinnear
Mr. Thomas Kinnear is considered a liberal gentleman. He has never married and carries on with his housekeeper, which causes him to be rejected by polite society. For example, the wives of his friends will not come to his house for dinner. Mr. Kinnear is kind to Grace but leaves her employment up to Nancy Montgomery. James McDermott shoots Mr. Kinnear with a shotgun, which he saw as a favor to Grace.
James McDermott
By all accounts, James McDermott is a surly, angry man. He had hoped to be a personal servant to Mr. Thomas Kinnear and dislikes being "set over by a woman." He is an agile dancer. He claims Grace put him up to the murders, while Grace says he forced her to be his accomplice and that she only went along with him because she was afraid of him.
Mary Whitney
When Grace first meets Mary Whitney, Mary is a buoyant, friendly fellow servant girl who shows Grace the ways of the household. Grace depicts her as bold and outspoken, holding rebellious views and using coarse language. After the master's son stays too long in the house, Grace notices a change in Mary, who becomes withdrawn. Grace knows the signs of pregnancy and confronts Mary, who admits she slept with a gentleman who gave her a ring but will not claim his child. Seeing no better option, Mary gets a botched abortion and dies. After Mary dies, Grace forgets to open the window and believes she hears Mary telling her to "let [her] in." "Mary" appears during Grace's hypnotism, claiming to have borrowed Grace's "fleshly garment" to commit the murders. Mary Whitney is the alias that Grace uses after the murders.
Jeremiah
Jeremiah Pontelli is a friendly peddler whom Grace Marks first encounters with Mary Whitney at Mrs. Alderman Parkinson's. He sells Grace four buttons and gives her a fifth for good luck. He also tells her she has rocks in her future but all will turn out okay in the end. Once Grace ends up at Mr. Thomas Kinnear's, Jeremiah visits her there and tells her she is in danger. He offers to take her away with him but stops short of an offer of marriage, so she refuses. Later, he appears as his alias Dr. Jerome DuPont and performs the hypnotism on Grace.