In "The Witness for the Prosecution," the protagonist, Leonard Vole, has been charged with the murder of the immensely wealthy Emily French. The text tells us that Emily bequeathed the bulk of her fortune to Leonard before her death.
The antagonist is the enigmatic Romaine Vole. For her part, Romaine is an interesting antagonist. While claiming to oppose Leonard's interests, she actively works on his behalf.
In the story, Leonard is a static character. He portrays himself as a misguided but well-meaning young man. In actuality, Leonard is an impostor. He takes on a boy-next-door persona to deceive his solicitor, Mr. Mayherne, who does not realize that his client is engaging in a cynical act of deception. When questioned by Mr. Mayherne, Leonard disarms the latter with his quiet earnestness.
Leonard openly admits that his case looks bleak. He even acknowledges the unpleasant rumors surrounding his unusual relationship with Emily. Throughout his interaction with Mr. Mayherne, Leonard portrays himself as a sincere but flawed individual. He ingratiates himself to the solicitor. Leonard tells Mr. Mayherne that he has a "weak nature" and that he found it difficult to ignore the pleadings of a "lonely" and "unhappy" old lady.
Then, Leonard openly admits to a secret fascination with being "mothered." In light of the prevailing culture, his confession would be seen as an embarrassing one. However, he willingly shows his vulnerable side to Mr. Mayherne. In response, the solicitor begins to trust Leonard (his biggest mistake) and becomes protective of his young client. Leonard's trusting nature, albeit an act, disarms the solicitor. Christie uses indirect characterization, the interactions between Mr. Mayherne and Leonard, and the interactions between Mr. Mayherne and Romaine to foreshadow the stunning ending.
Throughout his interaction with Mr. Mayherne, Leonard is shown to be a master manipulator. Earlier in the story, the third-person omniscient narrator makes it a point to emphasize Mr. Mayherne's supposedly shrewd character. The solicitor is said to be "by no means a fool." However, Mr. Mayherne is fooled not just by Leonard but also by Romaine Vole. Both Leonard and Romaine play their roles to perfection.
Leonard's boy-next-door persona prepares the way for the dynamic Romaine, who does not bother to hide her supposed disdain for her husband. After Leonard's performance as a seemingly insipid "Mama's boy," Mr. Mayherne is thrown off guard by Romaine's clearly visceral hatred for Leonard. Additionally, her vicious accusations and hysterical behavior immediately raises the solicitor's suspicions about her mental state.
In the story, the author makes it a point to emphasize Mr. Mayherne's "cool and unemotional" character. Such a character would be repelled by any undue displays of emotion and would characteristically revert to type in the face of such emotion. In fact, Mr. Mayherne is the type of man who would also be repelled by women who emphasize the "stupidity of men" and who use derogatory epithets to reference men.
Romaine's performance as an old hag is equally masterful. Her repellent features and fiendish behavior further solidifies Mr. Mayherne's earlier perception of Romaine. Here, the author uses dramatic irony to further the plot line. We suspect that Mr. Mayherne is being taken in by Leonard and Romaine, but the solicitor is oblivious to the deception the two are foisting on him. Indeed, Romaine manages to drive Mr. Mayherne's sympathies toward Leonard, which was her goal all along. The story highlights the themes of deceptive appearances, self-serving loyalty, misguided trust, and greed.
Both Leonard and Romaine conspire together to fulfill the dictates of their greed. They also remain loyal to one another, and they are united by their mission to deceive the well-meaning solicitor. We are little surprised at Romaine's final "you do not see at all. I knew—he was guilty!" Indeed, we hear the echoes of her previous words: "How stupid men are! Stupid—stupid—stupid."