Excerpted from Wikipedia
In the rainy November of 1932, the snobbish Constance, Countess of Trentham and her young, inexperienced and timid Scottish maid Mary MacEachran travel by car from the Countess' estate to Gosford Park, a country estate belonging to the Countess' niece and nephew-in-law for a weekend shooting party. On the way there, they encounter another party also on their way to Gosford Park: the matinée idol Ivor Novello, his friend, Hollywood producer Morris Weissman and Henry Denton, Morris Weissman's valet. Upon their arrival, the guests are greeted by Sir William McCordle, his rather younger wife and the Countess' niece, Lady Sylvia McCordle, and their daughter Isobel.
Besides the Countess, Mr Novello and Mr Weissman, the “upstairs” guests include Lady Sylvia's sisters Louisa and Lavinia; their respective husbands, Lord Raymond Stockbridge and Commander Anthony Meredith; the Honourable Freddie Nesbitt and his "common" wife Mabel; Isobel's suitor Lord Rupert Standish and his friend Mr Jeremy Blond. Lord Standish and Mr Blond arrive during dinner service on the first evening, considerably later than the other guests.
The Nesbitts' official association with the McCordles is not established with any certainty; the couple is also noticeably without ladies' maid or valet. Mr Nesbitt has married with an eye to his wife's father's money, made from the manufacture of gloves; the money is now gone and the Nesbitts are in dire financial straits. In secret, Mr Nesbitt is blackmailing Isobel with some past secret of hers in an effort to gain her assistance in procuring employment from Sir William. His behaviour seems to indicate that at one time, he had seduced Isobel; it is later revealed that the secret Mr Nesbitt is using to blackmail Isobel is a pregnancy which was kept secret from her parents. It is not clear whether or not the child was Mr Nesbitt's, although the inference that Isobel had been seduced by him makes it likely. It is also inferred, but never clearly stated, that the child was aborted before Isobel's parents might have independently discovered the affair.
Mrs Nesbitt becomes convinced by her husband's behaviour that her husband is seeking to re-establish the liaison while here, a conviction fueled by the derision directed at her by her husband and his ennobled acquaintances among the party. Her position as someone to be ridiculed by the party, in behaviour by most and openly by Lady Trentham, is further established by the fact that she has only brought one dress for evening. Disclaiming that she was rushed during packing by her husband and only brought one by mistake, it is later hinted that she only possesses one evening dress.
Another internal conflict among the upstairs guests is that Sir William and Commander Meredith are also in financial difficulty; an expedition to provide supplies and modern equipment to the Sudanese army is the Commander's last chance to avoid financial ruin, and Sir William's investment in the project is crucial to its success. Sir William intends to rescind his agreement to invest, and also intended to disclose that to the Commander the following week, after the shooting party. Commander Meredith's insistence in bringing up the matter after a chance word between he and Isobel during the first evening's dinner causes Sir William's intentions to be revealed early. Lady Lavinia is supportive of her husband, whom she apparently married for love, and angry with her sisters that they will not use their influence to change Sir William's mind.
Lady Trentham is stated to receive an allowance from Sir William; how often the payments are made and the size of the allowance is not established, but it is Lady Trentham and Lady Sylvia's understanding that it would be paid for the remainder of Lady Trentham's lifetime. Sir William comments to his wife before dinner the first evening that he is of a mind to stop paying the allowance entirely if Lady Trentham asks him for more money during the weekend, which Lady Sylvia warns her aunt about prior to dinner on the second night.
Lady Sylvia and Lady Louisa appear to be married to exactly the opposite sort of man than would suit either of them; discussion amongst the servants reveals that Lord Carton, the sisters' father, was intent to have Sir William marry one of his elder two daughters but didn't care which daughter married him. Lady Sylvia and Lady Louisa "cut cards" for the “privilege”, and Lady Sylvia won. It is blatantly apparent that Lady Louisa and Sir William are having an affair, and that Lady Sylvia would like to have one with Lord Stockbridge, who seems to rebuff her more serious attempts to flirt or invite such a liaison.
Mr Weissman, who produces Charlie Chan mystery movies, is intent on conducting pre-production business for his newest film, “Charlie Chan in London”, over the course of the weekend. He appears to be encountering serious opposition to his casting and writing preferences on the film, and presents great annoyance to the English guests by placing several “urgent” calls to California. Mr Novello, who is Sir William's maternal first cousin once-removed, agreed to provide musical entertainment in the evenings in exchange for Sir William allowing Mr Weissman to come and observe a shooting weekend; Mr Weissman intends to use his observations to make the new film's setting more realistic, as it will also be set at an English country estate during a shooting weekend.
Mary and Parks are instantly attracted to one another upon first meeting. Parks subtly flirts with Mary during many conversations over their duties. Over the course of the weekend, Mary's inexperience is highlighted, although she is influenced in several ways by Parks, Mrs Wilson, Elsie and the circumstances in general and has a better understanding of what is expected of her by the end of the film.
Denton, whose faux Scottish accent is noticed by nearly all the servant staff, is slightly better at covering his inexperience due to his appearance of smooth confidence. He asks a number of questions which gives the other servants pause, including asking the assembled staff at dinner on the first night who among them had parents in service, and whether or not it influenced their own decision to go into service. Several at the table raise their hands as having parents in service; Barnes states his parents were factory workers and he felt they had better positions than he. Dorothy claims that her parents were farmers and tenants of Lady Sylvia's father, Lord Carton. Initially reluctant to give details, Parks indicates that he knows the occupations of his parents, but that knowledge did not influence his own decision to enter service, as he was raised in an orphanage outside London.
At that same dinner, Lady Sylvia meets Denton and is quite taken with his youthful handsomeness when she comes to inform Mrs Wilson that Morris Weissman is a vegetarian. Mrs Wilson informs her that Denton had already informed her and Mrs Croft upon arriving at Gosford Park.
The first evening sees Sir William arrange for Elsie to come to him that evening with a careful glance and avoid allowing Lady Trentham to have a private word regarding her allowance. Bertha catching the eye of Mr Blond upon their arrival and Lady Trentham reveals to Mary that Lady Sylvia and Lady Louisa cut cards for the honor of marrying Sir William. Denton attempts to rape Mary in the room he shares with Parks, though Parks interrupts; Denton later arranges an interlude with Lady Sylvia, taking advantage of her attraction to him. When going down to wash a shirt for Lady Trentham late in the evening, Mary interrupts the interlude between Mr Blond and Bertha by walking into the next room and turning on the light, although Mary believes it is Sir William. Before dinner, the Nesbitts bitterly quarrel and Mr Nesbitt nearly becomes physically violent with his wife, but Elsie comes back from seeking hairpins for Mrs Nesbitt and interrupts the argument.
The next day is a pheasant hunt: while the gentlemen go out with the various hunting servants (beaters, dog handlers and loaders), the ladies linger in Lady Trentham's rooms, with the exception of Isobel and Mrs Nesbitt. Lady Lavinia upbraids her sisters for not trying harder to help her and her husband by preventing Sir William's investment withdrawal. The tension between Lady Sylvia and her daughter becomes evident when Isobel comes in to say the cars are ready to take the ladies out to the gazebo pavilion for luncheon: Lady Sylvia expresses dismay at what Isobel is wearing, to which Isobel snaps back that Lady Sylvia herself purchased the outfit. Lady Trentham cuts another insult to Mrs Nesbitt's fashion sense, whom Lady Lavinia then defends.
During the hunt, Sir William's ear is grazed by a stray shot. No one is certain who fired it, although Mr Novello, Mr Weissman and Denton are not suspects because they are sitting aside observing and not carrying guns. During luncheon service, Commander Meredith tries to quietly plead with Sir William not to back out of the investment and, in desperation, causes him to drop a glass and alerts the entire party to the argument.
Just prior to dinner, while dressing for the evening, Lady Trentham insists upon knowing the servants' gossip about the Commander's situation, telling Mary that she only requires discretion about her own affairs in a ladies' maid. During the dinner service, Lady Sylvia attacks Sir William's character out of anger, implying that he was a profiteer during the war, that it was out of cowardice that he did not go into the armed services, and that all he is interested in is money and guns. Elsie, who had become fond of Sir William during their liaison because he talked to her like a person, loses her temper and snaps at Lady Sylvia, betraying the affair with her start of a defense for Sir William and calling him “Billy”. Knowing that this is grounds for immediate dismissal, Elsie stares Lady Sylvia down for a moment and then leaves the dining room before anyone can verbally respond. Sir William angrily closets himself in the library and the other guests adjourn to the dining room; Lady Sylvia confides in her sisters that she knew about the affair, and this has given her the excuse she needed to dismiss Elsie. She then asks Mr Novello to play while the party clusters in the drawing room to converse and play bridge.
The servants cluster in the dining hall to hear what happened from those who were serving. Jennings disperses them, particularly reprimanding George and Dorothy. Eventually, listening to Mr Novello playing and singing at the piano, the servants cluster in various doorways to listen. Denton goes up to Elsie's room to offer a drink and sexual comfort, but she rebuffs him, having no interest. Mrs Wilson comes into the library bringing Sir William a cup of coffee while he cleans his guns. In a fit of anger, he knocks it out of her hand and demands a glass of whiskey.
While Mr Novello plays, four people disappear: Parks, George, Mr Nesbitt and Commander Meredith. Intercut with images of the servants enjoying the music in many different parts of the house, an unknown man slips out, puts on muddy over-shoes and removes a missing silver carving knife from where it was hidden in a fire bucket. Only black-trouser-clad legs are visible to the viewer. The man goes to the library and stabs Sir William in the chest, pushing the body over. All four missing men then reappear: Commander Meredith and Mr Nesbitt do not offer an explanation of their disappearances; George was ostensibly fetching more milk for the coffee service, though he begged a cigarette from another servant, but was gone far too long for Jennings' liking; and Parks was fetching and filling the hot water bottles both he and Mary would need for their employers later.
Lady Sylvia despairs of talking to Sir William about the incident and defusing his anger; she asks Lady Louisa to try, declaring that Sir William has always preferred Louisa to Sylvia. Lady Louisa enters the study and finds Sir William slumped over the desk. Initially believing him to be asleep, she approaches and discovers he is dead. Her hysterical screams bring gentry and servants alike to the library, where Lord Standish attempts to keep Isobel out of the room, Lady Lavinia faints, Lady Louisa is passed off to another man in her hysteria and Lady Sylvia stumbles to a couch and sits down in numb shock. After assessing the situation, Lord Stockbridge steps out, hangs the phone up on Mr Weissman (who was on the phone with someone in California at the time and did not even abandon his conversation when Lady Louisa began screaming hysterically in the next room), and then calls the local constabulary.
A short time later, Inspector Thompson and Constable Dexter, along with several others, arrive to begin investigating the situation. The inspector's competent assistant notices that there is little blood coming from the stab wound, suggesting that Sir William was already dead when he was stabbed. The inspector makes several procedural errors in that initial evening, including allowing Lady Sylvia to interrupt him and to make introductions, ignoring Constable Dexter's observations, having Probert brought up into the library before the body is examined and removed to answer questions, and allowing Probert to sit Sir William up, revealing the knife buried in his chest.
The various servants are informed that the Inspector and constables will not allow anyone to leave, including Elsie, whom Mrs Wilson orders to remain in her rooms until the house arrest is lifted. Denton confesses his real background to Jennings, and it quickly makes the rounds among the servants. Jennings immediately moves him out of the servants' quarters and into his own room, as he should not be treated as a valet but as a guest. Denton offers consolation to Lady Sylvia, who does not know he is an American yet.
The next morning, Lady Sylvia goes for her usual morning ride after breakfasting in her room in violation of the house arrest. Inspector Thompson is surprised by this, clearly not having anticipated that the widow would not be prostrate with grief above-stairs. The other guests sit down to a breakfast buffet, including Mr Denton, who now makes no pretence of being a servant and whom Jennings treats with dismissive contempt. Jennings also reassigns George as valet to Mr Weissman as well as Lord Standish, and Parks volunteers as valet to Mr Novello after Jennings refuses to add him to Arthur's duties. Mr Denton is not assigned a valet out of contempt for his subterfuge.
Inspector Thompson begins to question the upstairs guests over the course of the day: Lady Trentham is asked about her allowance, which is no longer in danger of being revoked now that Sir William is dead. Mary is also asked if she knows anything about the disagreement over the allowance while Lady Trentham is present (another breach of police procedure); she impresses Lady Trentham by denying any knowledge of the allowance whatsoever and stating that Lady Trentham and Sir William got on well. Lord Stockbridge is asked about the low shot that grazed Sir William the day before, about which he withholds details: he in fact knows that Commander Meredith fired the shot, but did not disclose that to the Inspector because he believed it to be an accident owing to the Commander's short stature. Barnes, however, overhears Commander Meredith tell Lady Lavinia that Sir William's death was a lucky thing for them, as the investment Sir William promised is now also secure; he discloses it to Inspector Thompson out of contempt for his employer, who is then interrogated at length over the low shot due to his apparent motive.
Elsie has snuck into Isobel's room to talk with her, having become the girl's confidante. She shows Elsie a note left by Mr Nesbitt during his disappearance from the drawing room threatening to reveal her secret if Sir William does not provide him with a job. Elsie comments on how stupid the note was. Isobel then asks if Elsie will be all right and if she is “in trouble” (pregnant). Elsie tells her that she is not pregnant, but she expects to manage just fine once she leaves. Later, still being pressed by Mr Nesbitt, Isobel writes him a cheque. Mrs Nesbitt, who sees the exchange, demands to know what Isobel gave him. Her husband shows it to her and then tears it up in a fit of rage over his wife's questioning him, declaring that she can buy herself a new dress with the fragments.
Commander Meredith spends dinner hiding in the pantry below stairs, eating jams and wondering about why some men are lucky financially and some aren't, though not for lack of trying. After asking Dorothy about the idea, she replies fervently that she believes love is the only thing that matters, even if it is not reciprocated. Commander Meredith mulls this for a moment, applies the idea to his own situation due to the love-match he enjoys with Lady Lavinia, and goes up to join the party in the drawing room. Mr Denton is also in the drawing room, having been refused even an opportunity to explain or apologize for his actions to the staff. George dumps hot coffee in Denton's lap as an act of revenge.
Having formally interviewed only three servants (Mrs Croft, Mary and Barnes), Inspector Thompson announces to the servants that the party will be allowed to leave in the morning, as the servants had no “real connection with the dead man” and therefore need not be questioned. The servants appear stunned by this idea, but are relieved that their duties will not be unduly overburdened by a lengthy house arrest of the shooting party.
That night Elsie tells Mary how she did not love Sir William but did not mind him. She also tells Mary what Sir William used to tell her: "Carpe diem, seize the day." Inspired by this statement, Mary runs to Parks' room. She there confesses her disbelief at the idea that Parks could have been the one to murder Sir William, declaring that Parks would have had to hate Sir William and they had never met before this weekend. Parks replies with a question: “Can't a man hate his own father?”
His further explanation of his motive is interwoven with an exposition given to Bertha by Mrs Croft earlier in the day: Parks' mother worked in one of Sir William's factories some thirty years earlier, and Sir William had a reputation for seducing the female factory workers. If a woman became pregnant and had the baby, Sir William offered two choices: keep the baby and lose your job, or give the baby up and keep your job. Those who gave up their babies to save their jobs were told that the adoptions were being privately arranged by Sir William with good families of his acquaintance. According to Parks, that was a deception; in reality, Sir William was paying off those who ran the orphanages to take the children and keep their paternity secret. Parks discovered his father's identity just before his 18th birthday, when, as part of a group, he broke into the administration office to see his file. He entered service and worked his way up in an attempt to gain employment with someone in Sir William's circle of acquaintance and thereby an opportunity to kill him.
Mary is shocked at the cold-blooded premeditation, numbly asking why Parks chose poison. When Parks tells her that he didn't poison Sir William, Mary has a moment of wild hope that Parks stabbed him only because he knew Sir William was dead, but Parks gently disabuses her of the notion. He then passionately kisses Mary, who returns the embrace, but leaves when the kiss ends, shaken by what she has learned.
The next day Lady Sylvia returns from her morning ride to find that the Stockbridges, Lady Trentham, Mr Novello and Mr Weissman are still in residence but are preparing to leave; the Merediths, the Nesbitts, Lord Standish and Mr Blond have already left. As they are leaving, Isobel overhears Mr Blond telling Lord Standish that he can do better than Isobel because he would have to wait too long to get his hands on the McCordle money, as Lady Sylvia is now in charge of the estate. Isobel tearfully ends the courtship between herself and Lord Standish, thinking he was only interested in her for her father's money; Lord Standish was genuinely interested in Isobel, and leaves Gosford Park angry and hurt because his friend's comment had caused Isobel to think otherwise.
Coming to her aunt's rooms, Lady Sylvia and Lady Trentham discuss what she intends to do with the house, and the conversation drifts to speculation over why Mrs Croft and Mrs Wilson are such bitter enemies. Mary listens as Lady Sylvia tells her aunt that Mrs Croft used to be a cook in one of William's factories, apparently a higher rank than factory line worker, which was Mrs Wilson's position in the same factory. It is Lady Sylvia's belief that the tension between them stems from the fact that Mrs Wilson now outranks Mrs Croft. Lady Trentham asks if Mrs Wilson was ever married; Lady Sylvia replies that she must have been, as her name was “Parks or Parker or something like that” when she worked in the factory.
Slipping downstairs as the final guests are preparing to leave, Mary openly asks Mrs Wilson how she knew Robert was her son. Initially avoiding a direct answer, Mrs Wilson avoids the question but admits that she saw the picture of his mother on his nightstand. She in time reveals that she and Mrs Croft are sisters, that the enmity between them really has two causes: 1) that she gave her child up, while her sister kept hers and lost her job; and 2) that when her sister's child died from scarlet fever, she made Sir William give her sister her job back. Mrs Croft had never forgiven her sister for either.
Mrs Wilson then reveals, at Mary's prompting, that she anticipated her son's homicidal intentions, and that by poisoning Sir William herself, she had removed her son from danger: there isn't much of a crime in stabbing a dead man, and therefore, the authorities would not pursue him when investigating the death. She also informs Mary that good servants must possess the gift of anticipation, and that she is the perfect servant: she knows when others will need something before they themselves know, and it is presented precisely when necessary… and she has no life of her own; therefore, she has nothing to lose if she is discovered by the authorities to be the murderess. Mary asks if Mrs Wilson will tell Parks that she is his mother; Mrs Wilson avoids the question, asking instead what purpose Mary thinks it would serve for him to know. Mary, contemplating everything she has learned, goes to meet the car and Lady Trentham.
Stepping into her own room after a brief word with Dorothy, Mrs Wilson loses her unflappable composure and dissolves into hysterical sobs. Mrs Croft comes in to comfort her, offering forgiveness by telling her that at least her child is alive, and that Mrs Croft realizes Mrs Wilson was only doing what she felt was best for her child.
She bids farewell to Elsie and Parks, noting with some amusement that Elsie is taking Sir Williams' dog with her (Lady Sylvia had always hated the dog, kicking it at one point during the movie). Lady Trentham worries that she or Mary might have to testify at a trial, and speculates with horror over the notion of someone being hanged due to such testimony. Mary echoes Mrs Wilson's sentiment, rhetorically asking what purpose it would serve. This answer apparently reassures Lady Trentham, and the movie closes with Lady Sylvia re-entering Gosford Park and Jennings closing the door.