Set in a small Northeastern community, By Love Possessed chronicles forty-nine hours in the life of Arthur Winner, Jr., a respected lawyer and citizen of Brocton. The title refers to the different types of love—sexual love, parental love, friendship, love for community and church—which play a part in Winner’s life as a man and as a lawyer. The novel opens as Winner contemplates the clock in his mother’s house with the inscription omnia vincit amor. Winner has patterned himself after his deceased father, the “Man of Reason,” and the conflict between love or passion and reason dominates the action.

As the defense attorney in a rape case against eighteen-year-old Ralph Detweiler, the much younger brother of Helen Detweiler, a legal secretary in the firm of Winner, Tuttle, and Penrose, Winner attempts to apply reason and logic to the emotionally charged situation. The case is complicated by the fact that, although Ralph admits having had intimate relations with Veronica Kovacs, a young woman with a tarnished reputation, he also admits being involved with Joan Moore, whom he has gotten pregnant. Winner assures Ralph that the charge of rape will almost certainly be dropped, but the immature, spoiled Ralph panics at the thought of facing a trial and a pregnant girlfriend. He jumps bail and in the process steals money from one of the boarders in Helen’s rooming house. Helen, having reared Ralph since their parents’ death in a tragic boating accident, sees all of her plans for Ralph’s future collapse, and she commits suicide. Winner’s reasoned approach is thwarted by people tangled in passions, and he is unable to prevent tragedy.

After Helen Detweiler’s death, Winner visits the law office to obtain her will and accidentally uncovers evidence that sets another conflict in motion. Noah Tuttle, the eighty-year-old senior partner of the law firm and a man of unquestioned integrity, has been misappropriating funds over a number of years to protect local investors from financial ruin as a result of the collapse of the Brocton Rapid Transit Company, which he had recommended as an investment. When Winner presents Julius Penrose with this discovery, he learns that Penrose has been aware of the situation for more than ten years and has chosen to keep silent and give Tuttle the chance to replace the money. The Orcutt trust, a fund designated for use by the Episcopal Church of Brocton (where Winner is a prominent layman), is also involved.

Winner knows that his father, the “Man of Reason,” would have immediately done the “right thing” and turned Noah over to the authorities, thus destroying all the members of the firm professionally as well as financially. Penrose persuades Winner that Noah has acted out of love: “He would betray himself, sacrifice himself, before he let down, sacrificed, those who had put faith in him.” During this tense discussion, Winner makes another discovery. Although he prides himself on his ability to act on reason, shortly after the death of his first wife he succumbed to passion during a brief, but intense, affair with Penrose’s wife, Marjorie, and—Winner now realizes—Penrose has been aware of this affair since its inception.

Winner’s simplistic moral code is challenged by Penrose’s deeper understanding of moral complexity; Penrose persuades him that the strict honesty which would demand revealing Tuttle’s deeds is not the best policy but only the easiest one. Their duty, like Tuttle’s, lies in doing what is necessary to protect their community. Winner learns that what seems a clear choice, with freedom to act, is often no choice at all but merely the acceptance of a fate that has been predetermined. He recognizes the truth in his brother-in-law Fred Dealey’s words: “Freedom is the knowledge of necessity.” Winner’s faith in reason has been tempered by the effects of passion, and he now asserts that “Victory is not in reaching certainties or solving mysteries; victory is in making do with uncertainties, in supporting mysteries.”