The protagonist of The Man of Mode is Dorimant, a notorious libertine and man-about-town.
The story opens with Dorimant addressing a billet-doux to Mrs. Loveit, with whom he is having an affair, to lie about his whereabouts. An "Orange-Woman" is let in and informs him about the arrival in London of a beautiful heiress – later known to be Harriet. Dorimant's closest friend and fellow rake Medley arrives, offers more information on her. Dorimant expresses his wish to break off his relationship with Mrs. Loveit, being already involved with her younger friend Bellinda. The two friends plot to encourage Mrs. Loveit's jealousy so that she will break off the relationship with Dorimant. Young Bellair, the handsome acquaintance of both men, enters and relates his infatuation with Emilia, a woman serving as companion to Lady Townley—his devotion is ridiculed. The three debate the fop Sir Fopling Flutter, newly come to London. Bellair learns of his father's arrival, that he lodges in the same place as his Emilia and of his desire for a different match for his son. A letter arrives from Mrs. Loveit and Dorimant departs.
Lady Townley and Emilia discuss the affairs of town, particularly Old Bellair's professing of love for Emilia and his lack of awareness about his son's own affections for her; he intends instead for him to marry Harriet. Young Bellair admits to having written a letter promising his acquiescence to his father's will in due time so as to deceive him. Medley arrives and boasts to the ladies of Dorimant's womanising status.
Mrs. Loveit becomes enraged with jealousy at Dorimant's lack of attention to her, while her woman, Pert, attempts to dissuage her from such feelings. Bellinda enters and informs her of a masked woman that Dorimant was seen in public with. Dorimant appears and accuses the women of spying on him, and also that Mrs. Loveit has encouraged the affections of Sir Fopling; in a pretended state of jealousy, he leaves.
Harriet and Young Bellair act as if they are in love to trick the onlooking Lady Woodvill and Old Bellair. Meanwhile, Dorimant and Bellinda meet at Lady Townley's and arrange an imminent meeting. Emilia then reveals her interest in Dorimant to Bellinda and Lady Townley. Bellinda persuades Mrs. Loveit, on Dorimant's request, to take a walk on The Mall and thereby be 'caught' in the act of flirting with Fopling. Dorimant meets with Fopling, and pretends that Mrs. Loveit has affections for him (Fopling). When Mrs. Loveit encounters Fopling she acts flirtatious, in spite of not liking him, and succeeds in making Dorimant jealous. Medley suggests he attends a dance at Lady Townley's which Harriet will be, though in the disguise of "Mr Courtage", to take his mind off Mrs. Loveit. Woodvill chides Dorimant and his reputation in front of him, not seeing through his disguise. Dorimant admits to Emilia that he loves Harriet, but continues to be obstinate. Fopling appears and almost uncovers Dorimant, but the latter leaves to meet Bellinda. Once there, she expresses her jealousy at Mrs. Loveit, imploring him to never see her again. Meanwhile, Young Bellair discovers his father's affections for Emilia, and Harriet's for Dorimant, and informs Dorimant of this.
Bellinda returns to Mrs. Loveit's in the early hours, but, taking the same hired chair that Mrs. Loveit had taken when she left Dorimant's, is suspected of being up to something. Dorimant arrives afterwards and confronts Mrs. Loveit. She says she is aware that he is only faking jealousy to spend time with another woman.