Emily Johnson lives in a furnished room, within a building that houses many other similar rooms. Though married, her husband is in the army, and Emily works in New York. She has lived in the room for six weeks, and during the most recent two weeks, she has noticed that small articles from her room are missing. Among the items missing are handkerchiefs, a pin, and a bottle of perfume. Emily hesitates to tell her landlord of this issue, because she believes she will be able to handle the situation and discover the identity of the thief. In fact, Emily suspects that the thief is the only person in the building who remains at home every day—and catches the thief exiting her room one Sunday.
Finally, one night, Emily decides to confront the thief. She knocks on the door of Mrs. Allen. Mrs. Allen’s “room, Emily noticed immediately, was almost like her own” (35). Mrs. Allen is over twice as old as Emily. The two women chat briefly, and Emily learns that Mrs. Allen’s husband was also in the army, but died five years ago. The Allens never had any children, but Mrs. Allen keeps photographs of her nieces and nephews. Emily comments on Mrs. Allen’s flowers, and the latter informs Emily that dropping aspirin in flower water helps them grow.
Emily is eventually able to confront Mrs. Allen about her missing items, though indirectly. She explains the situation to Mrs. Allen and hints that she knows who the perpetrator is, while assuring Mrs. Allen that she does not wish to raise the issue with the landlord. Emily simply expresses her desire for the pilfering to stop, with which Mrs. Allen agrees. Mrs. Allen informs her that the keys to all of the rooms in the building are interchangeable. Quickly thereafter, Mrs. Allen retires to bed. However, the next night, Emily returns from work to discover that a pair of earrings and a pack of cigarettes are missing. She considers the situation, writes a letter to her husband, and then decides upon a course of action. The next day, Emily calls in sick to work and remains at home. She listens for Mrs. Allen to leave the building and then lets herself into Mrs. Allen’s apartment.
In Mrs. Allen’s room, Emily lifts the shades and realizes how eerily similar Mrs. Allen’s apartment is to her own. “She had a sudden sense of unbearable intimacy with Mrs. Allen” (38). Emily surveys the closet, then the dresser, in which she finds all of her missing belongings neatly arranged in the top drawer. Next to her handkerchiefs are a box of Kleenex and a box of aspirin, for Mrs. Allen’s flowers.
As Emily counts her handkerchiefs, she realizes that Mrs. Allen stands in the doorway, watching her. Emily barely begins to explain herself to Mrs. Allen, who does not appear to be upset. Emily stares at the picture of the Allen couple. “They must have had such a pleasant life together, and now she has a room like mine” (39). Emily cannot bring herself to account for her presence in Mrs. Allen’s room, and instead she claims that she let herself in due to a bad headache and needed aspirin. Mrs. Allen graciously accepts her explanation, gives Emily aspirin, and advises her to take two and return to bed. Emily departs, and Mrs. Allen promises to check on her later.
Jackson underlines subtle similarities between Johnson and Allen, which ultimately explain why Johnson succumbs to her sympathy for Mrs. Allen and chooses not to reclaim her belongings. The moment at which Emily decides not to confront Mrs. Allen with the physical evidence that the latter is a thief, Emily notes similarities between her own life and Mrs. Allen's. First, both women's husbands are or were in the army, leaving them behind to live in a nondescript building with identical studios. The Allens never had children; Emily, too, is childless. These similarities cause Emily to align herself with Mrs. Allen and become, in a way, her twin.
Physical objects and locations described in the story also reinforce Jackson's suggestion that Mrs. Allen and Emily are “identity” twins. In particular, the items Mrs. Allen chooses to pilfer from Emily are symbols of the latter's identity. She steals Emily's handkerchiefs (such a highly personal item is often monogrammed) and her initial pin, which is more obviously a symbol. Jackson's description of the building also contributes to the sense of simultaneous anonymity and conformity achieved in the story. The studios are all identical, and each key fits each door. No privacy is established among the tenants, and their homes are eerily similar to one another in terms of setup and furniture. In other words, they are all facelessly the same. Mrs. Allen and Emily could be the same person, given that their homes, keys, and (due to Mrs. Allen's thievery) possessions are alike.
While Emily appears to be the protagonist, she and Mrs. Allen are ultimately in two different stages of the same life. Their identities are interchangeable, and they themselves, by not acting assertively, are complicit in allowing this to be so. The interchangeability of their lives is manifested by the similarity of their apartments. When Emily enters Mrs. Allen's apartment, "after she had opened the door, it seemed as though she were in her own room" (38). This is another example of a Jackson work in which the home (or apartment) represents the owner's identity and individuality (see "Like Mother Used to Make").
The external conflict in the story is clear. Mrs. Allen is sneaking into Emily's apartment during the day to steal her belongings. However, as in other Jackson stories, the true conflicts lie within the characters' minds. Emily fails to confront Mrs. Allen directly and retrieve her belongings. When she is caught snooping in Mrs. Allen's apartment, then, Mrs. Allen accepts her bald-faced lie as truth. They both avoid the necessary confrontation and thus, reality.
Some readers argue that "Trial by Combat" contains elements of the fantastic, that Mrs. Allen is a witch-like character. Read very literally as a standalone story, "Trial by Combat" could appear to be a very normal and non-supernatural story. However, given Jackson's occasional forays into the realm of the fantastic, particularly in the context of this collection, a reading of Mrs. Allen as a less than straightforward character is plausible. Furthermore, her parting statement to Emily, which concludes the story, also has ominous undertones. "'I'll run up later today,' Mrs. Allen said, 'just to see how you feel'" (39). This is a subtle, discomforting, or even threatening reminder that Mrs. Allen has access to Emily's apartment and, thus, her identity.