A 17th century castle, near Macon, north of Lyons, in France, on a very rainy summer evening. The owner, the Comte (Count) Georges de Coustines (Jean Rochefort) is in the attic, putting numerous chamber pots under the leaks of the roof, helped by Martial, an old servant.Martial walks back down to the ancient-looking kitchen, where he gets his dinner from the young baroness Amélie (Marthe Keller), Georges' daughter. Even though she is in her early twenties, Amélie is already divorced, which created a bit of a scandal in her noble family.Then Amélie has to walk a very long distance from the kitchen to the dining-room to bring his dinner to the only guest of the castle, a middle-aged man, Monsieur Patin (Claude Piéplu), who is a militant communist and atheist and writes in an obscure local newspaper.We meet Georges' wife, Diane (Maria Schell), and Diane's mother, the Marquise, (Madeleine Renaud). Diane is a pretty woman in her forties. She is a bit of a flirt, and we can guess she likes men and sex. The Marquise is in her late sixties or early seventies. She is a mixture of old aristocracy and modern ideas. We also meet Jeanne (Clotilde Joano), Amélie's cousin. She is in her late twenties, and has never been married. She hardly says a word, and just sits behind her piano and plays most of the time. The Marquise thinks she is a bit of a prude, and there are things she doesn't want to mention in front of her, mostly things concerning sexual life.The Marquise would like to turn the old dilapidated castle into a palace hotel for rich adulterous couples ! But, unfortunately, their one and only guest is Monsieur Patin. The Marquise suggests to Amélie to try again to get Charlie to bring guests to the castle.Charlie (Xavier Gélin) is slightly older than Amélie, but he has know her since they both were children in the village. He owns a garage. He is and always has been in love with Amélie, who tells him that, if he sends some guests to the castle, she will give him what he always wanted her to give him !On a rainy road, a Jaguar is driven by Jean-Jacques Leroy-Martin (Jean-Pierre Marielle), a rich play-boy, who tries to look younger than he is. Seated next to him is Cookie (Tanya Lopert), a young girl Jean-Jacques picked up hitch-hiking on the roadside. She is not very pretty, she is not very bright, she is dressed in flashy clothes with very large sunglasses and she doesn't even seem to be much interested in men and sex.Jean-Jacques stops in Charlie's garage for petrol. While he is in the toilets, Charlie pretends to check oil and water levels on his car, but actually he cuts a few wire in the engine. The car doesn't start. Charlie «checks» again the engine and says he needs at least three or four days to repair the car. Then, in his own car, a Citroen «deux-chevaux», he brings the couple to the castle, where the Marquise welcomes them and gives them two expensive adjacent rooms.Next, Charlie brings a party of young Swedish tourists, who do not speak a word of French. Then a typical French middle-class family, the Passereau : husband, wife (Janine Berdin), two children, and the wife's father, all on their way to their holiday on the seaside.Charlie drives back to his garage to find a big black American car waiting for him and for petrol. Seated in the back, is a very elegant man, who calls himself Baron Cesar (Yves Montand). Actually he is a gangster, and, seated in the front, are his two henchmen, Max (Jacques Balutin) and Schwarz (Pierre Tornade). Charlie, like he had done before with the other cars, prevents the car from starting again and then tells Cesar that he only telephone available is at the castle. They all climb inside the small Citroen, Cesar carrying a black briefcase.It is dinner-time in the dining-room of the castle. Everyone is very elegantly dressed and Jeanne is playing the piano.Downstairs, Cesar walks in with his two henchmen, and climbs the main staircase to the first floor lobby, where he uses the telephone without bothering to ask permission to do it. He asks for a number in Torino, Italy, and is told by the operator he has to wait to be called back.The Marquise talks to him with Grande Dame manners, and tells him she is ready to call the police. Cesar answers back with charm and smooth talk. He walks into the dining-room, and when he sees a very attractive Diane in a splendid green dress, he starts dancing a beautiful waltz with her. Then everyone starts dancing. But they are interrupted by the telephone ringing.Cesar tells Louvanski, his accomplice waiting for him in Torino, about his car problem, but Louvanski answers that the plane is already on its way. Cesar tells him he will call him back the next day. He puts the telephone down and wishes good night to all the ladies, who can't take their eyes off him.In the Marquise's bedroom, the Marquise, Jeanne, Diane and Amélie are listening to the radio, which tells about a bank robbery in Macon. A hundred millions francs have been stolen (100 millions francs in 1967 would be 125 millions euros in 2014).They stop the radio and start talking about Cesar, whom they all fell in love with. To prevent Diane from having an affair with Cesar, the Marquise asks Amélie to go and have Charlie fix Cesar's car as soon as possible, so they can send this «devil» away.When Amélie tells Charlie about Cesar's car, he doesn't seem too pleased, because he knows it will take him all night to fix it. But when she tells him she will be waiting for him in his bed, he goes to work with a smile on his face.Meanwhile in the castle, Jean-Jacques is making Cookie wait at the locked door of his room, because he is taking care of his wig ! Cookie gets tired of asking him to open his door, and when, eventually, he opens it, she slams her door in his face. Jean-Jacques nervously snatches his wig away from his head and Cookie opens her door again !Early next morning, Charlie has just finished working on Cesar's car, but he is too tired to do anything with Amélie and he falls asleep. Amélie brings the car to Cesar, who pays his bill and drives away with his two henchmen. Jeanne, standing near the door of the castle, waves at Cesar, who looks at her with a pensive expression on his face.The car has just reached the village when they meet a police roadblock. They turn around, but they meet another roadblock a little further on the road. Cesar asked Schwarz to drive backward, while he gets out of the car and starts shooting at the policemen. The gearbox gets stuck in reverse, and the car, still driving backward, ends up in a big pond, where it disappears under water.The police has not seen the car diving into the pond, and they think it has escaped by another road. Cesar, who was hiding behind a wall, still carrying his precious briefcase, looks at the police going away, and starts walking across the fields.Meanwhile, in the castle, everyone is getting ready to go to the church Sunday service, except Monsieur Patin, who is a professional atheist, and Amélie, who has decided she doesn't believe in God anymore, and consequently watches the castle while her family is away.We see Charlie coming to the castle on his bicycle, and further away, across the fields, Cesar discreetly walking back to the castle. In her room, Amélie, with a pair of binoculars, is watching the Swedish tourists swimming naked and doesn't move when Charlie walks in her room and starts undressing her. But suddenly she sits up because she just saw Cesar coming back to the castle.She walks down in the hall of the castle, leaving Charlie in her room. Because she is hidden by a large pillar, Cesar doesn't see her when he walks into the hall, and asks for a number in Torino. As the telephone rings back, he notices Amélie and hides in a small room for privacy, but Amélie listens to his conversation with Louvanski, to whom he explains that he cannot leave the castle because of the police roadblocks. He asks Louvanski to come in the evening and land his plane on the wide meadow in front of the castle.As he walks out of the small room, he notices two gendarmes coming toward the castle. He hides again in the small room, leaving his briefcase on the counter. The gendarmes want to question Amélie about the bank robbery in Macon. Amélie discreetly peeks into Cesar's briefcase and sees the money.After the gendarmes' departure, Amélie asks Charlie to carry her on his bicycle to the church, leaving a perplexed Cesar in the castle.Inside the church, Amélie whispers what she has found about Cesar to her grandmother. The Marquise is first a bit shocked to know there is a gangster in her castle, then she decides to kill him and take the money back from him. She walks out of the church with Diane, Georges and Amélie, leaving Jeanne who plays the harmoniumBut, when they reach the castle, it is to find that the police is already there. A commissaire (Charles Mallet), who is a high-rank police officer, tells them that they are still looking for Cesar. The Marquise leaves the commissaire and goes in the park through the back door of the castle, but seeing nothing, comes back to the hall and tells the slightly surprised commissaire that she needs her binoculars to look at something cooking in the kitchen. With the binoculars, she sees Cesar coming back to the castle. She tells Diane to prevent Cesar from coming back and Georges to stay on the terrace and watch them with the binoculars.Then she comes back to the hall and the commissaire, who explains her that they have found the car with two dead bodies, but not Cesar.Meanwhile, Cesar is counting paces to make a perimeter for the landing of the plane, and keeps on walking toward the castle. Diane, lying in the grass, screams because «she's got an ant inside her dress» ! Cesar starts looking for the ant, fumbling inside Diane's dress.Meanwhile, the commissaire explains to the Marquise that they have found a receipt of the castle in the glove box of the drowned car, and then he asks why Amélie didn't say earlier to the gendarmes that Cesar had been staying in the castle. The Marquise quickly answers that her grand-daughter certainly fell in love with him. She slaps Amélie, who starts crying and tells her grandmother she doesn't know where Cesar is. The Marquise asks the commissaire to search the castle. The commissaire knows that Cesar is not in the castle anymore and he leaves the castle and the Marquise.As soon as the police is gone, the Marquise takes the binoculars to check on Diane who is flirting in the grass with Cesar. The Marquise rings the lunch bell, and Diane stands up and leave a disappointed Cesar.The Marquise goes to the greenhouse and pour a very powerful insecticide inside a sauce-boat. Coming out, she meets Cesar and Diane. She tells Cesar he could put his precious briefcase in the safe. She discreetly gives the sauce-boat to Georges and leads Cesar to a small room in the hall, where the safe is located. Cesar puts his briefcase in the safe, but keeps the key in his pocket.Coming out in the hall, Cesar smells food, and, lead by the Marquise, goes to the kitchen, where Georges is setting a lonely fish croquette on a tray. Cesar moves him away and starts setting the croquette. We then understand that Cesar in a very skilled chef. But when he puts the poisoned sauce on the croquette, the croquette explodes !A bit later, Georges is inside Amélie's bedroom, breaking the floor with a hammer and a chisel. Actually, Amélie's room is just above a small sitting-room, where the Marquise wants to organize a game of poker and sit Cesar just underneath a heavy chandelier. Georges is digging the floor to unhook the chandelier. He is also going to play some loud Wagner music, and when the Marquise will bang the ceiling with a broomstick, it will be the signal to unhook the chandelier.Charlie enters Amélie's room, but when he sees her father in the room, he goes down in the hall to meet Amélie.In the park, Monsieur Patin, Jean-Jacques et Mr Passereau are playing croquet. Cesar is talking to rapturous Cookie and Mrs Passereau, and telling them about the women he has known all over the world. Jeanne is also listening to him, but standing a little further away.Meanwhile, Diane is fixing two cups of coffee, one of them being poisoned. The Marquise calls Cesar and Jean-Jacques for a little game of poker. The two men sit down around the card table, but the Marquise moves them around, to be sure that Cesar is sitting right under the chandelier.The game starts, and, above them, Georges starts playing Wagner. Diane enters with the coffee. Cesar takes a cup (the non-poisoned one), drinks it and gives the other one to Jean-Jacques. Cesar wins the game, and mechanically takes the poisoned cup to drink it. But Diane screams and he puts the cup down. Diane says there is a rat in the room and Cesar stands up to look for the rat, but the Marquise forces him to sit down, and then climbs on a stepladder to bang the ceiling with her broom. But Cesar stands up again and starts looking around for the rat. He knocks on the floor to attract it. Georges thinks it is the Marquise's signal and unhook the chandelier, which falls on the card table, a few inches from Jean-Jacques, who drinks the poisoned coffee and immediately spits it out.Amélie and Charlie are flirting in the straw in a barn, when the Marquise barges in followed by Diane and Georges. She wants a saw, a ladder and a length of rope, for her new plan to kill Cesar.A bit later, in the forest around the castle, Diane, Amélie, Cesar and Jean-Jacques are playing tag. But Cesar, in his shirtsleeves, only plays this childish game to try to be alone with Diane. He eventually gets hold of Diane and kisses her, but she runs away, finds Amélie and tells her to get rid of Cesar. Amélie teases Cesar who follows her up a tree. But one of the branches of the tree had been partially sawed by Georges and Cesar falls in the river below. The flow of the river brings him under the wheel of a old watermill. We hear a loud snapping noise and the Marquise, Diane, Georges and Amélie think that Cesar is dead, and start crying.Actually, Cesar is not dead and further down on the river, he meets the Swedish tourists swimming naked in the river. He starts fooling around with them especially the girls !Meanwhile, in the castle, the Marquise wants to open the safe, but remembers that Cesar had taken the key. She tells Amélie to ask Charlie to bring the cars back and also some tools to open the safe.The guests are getting ready to leave the castle. Jean-Jacques meets Monsieur Patin, who tells him he had been in love for a long time with Jeanne. He was feeling ready to tell her about his love, but he thinks she is in love with someone else. Then all the guests say good-bye to the Marquise and leave the castle, except the Swedish tourists who are still swimming in the river.After the departure of the guests, the Marquise asks Charlie to open the safe. Charlie starts working, but warns the Marquise that it's not going to be an easy job.Meanwhile the Swedish tourists are coming back to the castle with Cesar. They climb into their car and drive away while Cesar walks into the castle to get his jacket and his hat.Meanwhile, Charlie is still trying unsuccessfully to open the safe. The Marquise thinks it would be better to try to open the back of the safe rather than the front. They all go in the next room, and close the door behind them. The Marquise shows Charlie exactly where he should start breaking to wall to reach the back of the safe.Meanwhile, Cesar, coming from the hall, walks into the safe room, opens the safe and takes his briefcase. He doesn't see Jeanne hidden in the hall and watching him.Meanwhile, Charlie succeeds in breaking the wall down, only to find the safe wide open and the briefcase gone.The night has come, and Cesar walks out of the castle, carrying a few camper gas lamps, which he starts setting around to make a runway for the plane. Jeanne follows him without being noticed by him, and she moves the lamps to different locations. When the plane tries to land on the meadow, it actually lands in the lake where it disappears underwater !Jeanne goes back in the music room of the castle, and starts playing the piano, when Cesar walks into the room.Meanwhile a very angry Marquise wants to sell the castle and buy a bistro. She wants to tell Jeanne about it. But, when she peeks inside the music room, she almost faints when she sees the supposedly dead Cesar talking with Jeanne.Inside the room, Cesar is telling Jeanne about himself, the real himself, that he is a gangster who hasn't done half of the things he pretends he has done. Jeanne answers that she doesn't care about who he really is, because he is the only man she has ever loved.The Marquise enters the music room with a big smile on her face and doesn't seem surprised to find Jeanne in Cesar's arms. She takes the briefcase and Cesar lets her do it.Three months later, the castle has become the four-star «Hotel du Grand Siècle». And Cesar is the well-known chef of the place, working in a very modern kitchen with a large team of cooks. The dining-room is full of very elegant guests, served by waiters with frock-coats.In the music room, Jeanne is playing the piano, while the Marquise, Diane and Amélie are doing nothing but listen to her, and wait for Cesar to do everything for them.