Tess McGill (Melanie Griffith) is a 30-year-old secretary at Petty Marsh, a Manhattan financial conglomerate. An ambitious hard worker, Tess's goal is to move out of the secretarial pool and into an executive position, but she faces numerous obstacles. Because her business degree was not acquired at a prestigious school, she cannot gain entry to her firm's training program for recent college graduates. She also attends speech classes to sophisticate her speaking voice. She confides in her best friend and co-worker Cynthia (Joan Cusack) on their daily ferry commute.Tess's supervisor, David Lutz (Oliver Platt), is aware that Tess is seeking to advance her career, and provides her with the phone number of his colleague Bob Speck (Kevin Spacey). Tess is disgusted to find that Speck is a lascivious and debauched cokehead who promptly tries to seduce her in his limousine, forcing her to flee the car. Furious with Lutz, Tess returns to the office and humiliates him by writing an insulting message to him on the office stock-ticker.Following this incident, Tess is reassigned to a new financial division for Petty Marsh. She becomes the secretary for the company's new mergers executive, Katharine Parker (Sigourney Weaver). Tess is mildly nervous but ultimately pleased to be working for a woman for the first time, and is surprised to learn that Katharine is slightly younger than her as well. Katharine welcomes Tess with apparent warmth, promising a supportive, communicative relationship, and encouraging her to come forward with any ideas.Tess happily describes her new boss to her live-in boyfriend, Mick (Alec Baldwin), and expresses enthusiasm about finally having a potential mentor to help develop her career. Mick remains largely uninterested in Tess's work ambitions, but Tess is not discouraged. She continues to observe Katharine's style and mannerisms, admiring her poise and fearless navigation of the male-dominated business community.Petty Marsh acquires a new client, Trask Industries, which has expressed interest in investing in television to acquire a media foothold. Intrigued, Tess does some research and concludes that Trask would benefit more from an initial investment in radio, due to reduced competition. She presents this idea to Katharine, who receives it with an indulgent smile and promises to pass it along. Soon afterward, she informs Tess that the notion was shot down, as Trask is dead-set on investing in TV.Katharine is preparing for a skiing vacation in Europe, and reveals to Tess that she expects her boyfriend Jack Trainer (Harrison Ford), a fellow executive, to propose marriage during the trip. In the meantime, Katharine gives Tess an inspiring pep talk, encouraging her not to wait for what she wants to fall into her lap, but to make it happen herself.Jack Trainer makes a last-minute excuse to Katharine and backs out of the skiing trip, but Katharine senses no lost interest on his part. While enjoying the vacation on her own, she breaks her leg on the slopes and calls Tess from the hospital with a flurry of instructions. Tess agrees to inform other executives that Katharine will be out of commission for a few weeks, to keep up with work communication, and to check up on Katharine's Manhattan townhouse. Tess is fascinated with Katharine's luxurious lifestyle, and explores Katharine's impressive closets, gadgets, and workout equipment. Having discovered a handheld tape recorder containing Katharine's personal voice memos, Tess learns that Katharine had, in fact, seen Tess's suggestion about Trask as valuable, and that it had clearly not been dismissed as Katharine had claimed. Katharine's home computer reveals a message to Jack Trainer, passing off Tess's idea as her own and suggesting they move forward with it. Tess is angry and hurt by the betrayal, and returns to her apartment, where she discovers Mick in bed with Doreen DiMucci (Elizabeth Whitcraft), a mutual friend. Disgusted, and ignoring Mick's contrived apologies, Tess storms out.With no other options, Tess takes up temporary residence at Katharine's house, informing only Cynthia of this information. Catalyzed by the pain of both betrayals, and taking to heart Katharine's ironic advice of "making it happen" for herself, Tess resolves to jump-start her career while she has Katharine's advantages at her disposal. Using Katharine's name, she sets up a meeting with executives from Dewey Stone and Company, a radio organization where Jack Trainer is employed, to discuss a possible merger deal with Trask. Tess finds Katharine's invitation to a party hosted by Dewey Stone, and plans to attend the party herself in order to introduce herself to Jack the night before the meeting. She has Cynthia give her a more sophisticated hairstyle, but panics when she realizes the dress she borrowed from Katharine's wardrobe is worth six thousand dollars. Cynthia obtains a bottle of Valium from Katharine's medicine cabinet, and Tess accepts one to calm her nerves.Tess arrives at the party, and realizes she has no idea what Jack Trainer looks like, or how to find him. Sitting at the bar to collect her thoughts, Jack Trainer himself notices her and invites her to share in a few rounds of tequila. She asks if he can point her toward Jack Trainer, but he slyly conceals his identity, and the two flirt and drink until Tess feels the combination of alcohol and Valium taking effect. She prepares to leave, asking Jack to bring her coat out to her while she hails a cab. When Jack arrives outside with her coat, he finds Tess nearly unconscious in the back of a taxi, unable to give directions to the driver. Jack takes her to his apartment, carries her upstairs, carefully removes her expensive dress, puts her to bed, and falls asleep himself.Tess wakes up in her underwear, with a stranger asleep beside her. Mortified, and assuming the encounter had turned sexual while she was intoxicated, she quickly dresses and slips out of the apartment before Jack awakens. Later that day, Tess is shocked when she attends the Dewey Stone meeting and finds herself face to face with the stranger from the previous night. They both keep their composure, and Tess introduces herself as a Petty Marsh executive rather than a secretary. Jack and his colleagues are intrigued by Tess's proposal, and agree to present it within their company and let her know if it can proceed.Tess returns to Katharine's office, bemoaning to Cynthia that she had made a fool of herself the previous night. Cynthia expresses concerns about the stressful toll Tess is enduring from her double life. To their great surprise, Jack arrives on the floor, asking to see Tess. Cynthia, posing as Tess's secretary, shows Jack in, and leaves them to talk in private. Tess demands to know what happened after the party, and Jack assures her that nothing sexual occurred, and that Dewey Stone is game to move forward with the Trask deal. He invites her to dinner to celebrate the merger, but Tess, despite a developing mutual attraction, declines.With her deal underway, Tess continues assuming the persona of an executive with Jack and his colleagues while assuring Katharine over the phone that everything is running as normal. Tess embraces her new role in the business world, but is faced with seeing Mick again when they both attend Cynthia's engagement party. They catch up, with Mick congratulating her on her professional success, but when Mick is pressured by other party goers (who are unaware of his infidelity) to propose to Tess on the spot, Tess coyly gives a non-committal answer. Mick angrily confronts her afterward, accusing her of embarrassing him and of having skewed priorities. Realizing that Mick had never genuinely supported her or valued her goals, Tess finally lets their relationship end for good.Tess and Jack plan to speak with Trask's CEO, Oren Trask (Philip Bosco), to pitch their merger to him directly. They manage to crash his daughter's wedding reception, and secure an appointment to discuss it further. The meeting goes well, and Tess and Jack, elated by their success, give into their attraction at last. After a night together, Jack receives a phone call from Katharine while Tess is in bed beside him. He admits to Tess that he had been seeing a woman for some time, but the relationship had deteriorated for him, and he has been struggling to find the right time to end it. Tess does not reveal her connection with Katharine, nor that she is merely a secretary.Katharine calls Tess with the news that she is finally being released from the hospital, and will be returning to Manhattan. Tess scrambles to tidy Katharine's house, and to prepare for the finalization of the Trask deal, which is scheduled for the same day that Katharine comes home. Tess manages to keep up with everything, and rushes to the roof of the Petty Marsh building where Katharine arrives by helicopter. She escorts Katharine home, and begins to worry about arriving to her meeting on time, as Katharine is attempting to saddle her with numerous errands and tasks.Katharine has arranged for Jack to visit her at home that afternoon, still convinced that he will propose to her. She has Tess help her change into lingerie, completely unaware that Tess and Jack are now in a relationship. While Tess runs out to pick up a prescription for Katharine, Jack arrives at the house, making rushed and awkward conversation with Katharine, who remains oblivious to his discomfort. Still too nervous to end the relationship outright, Jack joins her in a glass of champagne and quickly departs after she attempts to seduce him. Tess returns soon afterward, finding a disappointed Katharine moping in bed. Tess gives Katharine her prescription and hurries off to her meeting, but in her haste leaves her appointment book behind. Katharine reads through it, discovers that Tess has been meeting with Jack for both business and pleasure, and furiously pursues Tess to the Trask office.Tess meets Jack at the Trask boardroom, and the meeting begins. Oren Trask is happy with the merger, but before the deal is finalized, Katharine bursts through the door on crutches and exposes Tess as a mere secretary. Tess does not deny this, but attempts to defend herself against Katharine's accusations that Tess had stolen the idea for the merger. Realizing the other executives are being taken in by Katharine's manipulations, Tess tearfully gives up and excuses herself from the boardroom. Jack is shocked and upset, but Katharine wastes no time in continuing the deal herself.Soon afterward Tess attends Cynthia's wedding as the Maid of Honor. She again speaks to Mick, who is now openly in a relationship with Doreen. They wish each other well, and part amicably. With her best friend away on a honeymoon, her boss furious with her, and her budding relationship with Jack abruptly halted, Tess returns alone to Petty Marsh to clean out her desk, bidding farewell to her fellow secretaries. As Tess makes what she assumes is her last walk through the lobby, she encounters Jack, Katharine, Oren Trask, and several executives on their way to continue the deal. Tess confronts Katharine, no longer holding back her fury, and refuses to be cowed by Katharine's lies and dishonesty. Katharine presents herself as a victim of Tess's manipulation, while Tess assures Jack that, while she had lied about her job title, everything about their romance had been genuine. Oren Trask is still not convinced of Tess's story, but Jack asserts that Tess put the deal together, and that she should be heading the meeting. The group heads to Katharine's floor, with Jack, Tess, and Trask in a separate elevator. On the ride up, Tess explains the origins of her initial idea about the merger, and outlines the potential obstacles she had prepared for, as well as a number of thoughtful details that finally prove to Trask that Tess has true talent for business, and that the merger was indeed her brainchild. Approaching Katharine in front of her office, Trask asks her to explain the inspiration behind the deal she had allegedly constructed. Katharine is unable to provide a satisfactory answer, and though she attempts to stall, Trask takes great delight in dismissing her on the spot. After Katharine angrily stalks off, Trask compliments Tess on her gumption, and offers her an entry-level job at Trask Industries, which she happily accepts.By the time her new job starts, Tess is living with Jack. He packs her a lunch for her first day, and sends her off with pride and encouragement. Tess arrives at work, and sits at the secretary's desk outside the appointed office. The woman in the office, who had been using the telephone, introduces herself as Alice Baxter (Amy Aquino), and apologizes for using the office phone. Tess is confused until Alice clarifies that the office belongs to Tess, and that she, Alice, is her secretary. As Alice begins to review Tess's schedule, Tess begins to process the reality of her new job. She insists that Alice treat her as a colleague rather than a superior, and they start off on a positive note. Once she is alone in her office, taking in the view of the city from her window, she calls Cynthia and shares the news. Cynthia, receiving the call in the middle of the secretary pool at Petty Marsh, enthusiastically relays the news to her colleagues, who are delighted to hear that Tess has achieved her dream career at last.