Letters of Thanks concerns a case of supposed witchcraft and demon possession in Boston, 1688. The incident serves as a prelude to the more famous witch trials of Salem and Andover 4 years later. The Puritan Minster Cotton Mather, takes into his home a 13 year old girl, Martha Goodwin, recently cursed by condemned witch Goody Ann Glover. The intransigent "witch" is condemned to death on specter evidence. Mather strives to save her soul. Meanwhile he and members of his congregation work to release Glover's victim, Martha, from her supposed state of demon possession. His efforts work to the detriment of his reputation and the corruption of his home life, as will his influence over the Salem trials several years later.