When the film starts, we find a group of fleeing bums and illegal immigrants being rounded up in the middle of the night amidst dog barks, cries and shouts by uniformed police armed with with helmets, batons, guns, torches etc from a broken down house somewhere in France. Next we see Baptiste Cambière (Pierre Rochefort ) teaching mathematics in a classroom to a group of primary students. When the school term ends, we hear the school's principal asking Baptiste if he would like to continue teaching as a permanent teacher but was told that he preferred being a substitute teacher because it suited him better to be a temporary teacher as it allowed him to better explore how different people in different environment deal with life. Everybody leaves for a long weekend as it's Whitsunday or Pentecost (7th week after Easter) but Baptiste notices that Mathias (Mathias Brezot) a small kid of 8 was all alone, leaning against the front wall close to the school entrance kicking the air out of sheer boredom, waiting listlessly to be picked up long after everyone is gone. He got down from the classroom from the window of which he caught sight of Mathias just as he was preparing to leave . He asks Mathias who he's waiting for. Mathias says that it's his dad. He asks him if he telephoned his father and is told that he already did many times but got no reply. Baptiste asks him where he lives. He akes him home in his motor cycle. He finds Mathias' father there, apparently having a good time with a girl and was invited in. His father said he made a mistake thinking that it was the turn of Mathias's separated mother to fetch him home. Seeing that his father, a race driver at Monte Carlo and his girl were not too keen to look after Mathias over the long weekend, Baptiste offered to do so. At first Mathias's father half heartedly said he shouldn't bother Baptiste but then thanked him when Baptiste told that that it was not too much trouble. He allowed Baptiste to take Mathias away.
Mathias felt bored at his house having nothing to do. Baptiste offered to take him to the beach. When they were there, Mathias said that he did not like it there but that he knew a better beach a little further down.So off they went. When they arrived, Baptiste found that that where Mathias' mother Sandra (Louise Bourgoin) was working as a waitress at a seaside restaurant. Sandra was surprised and invited Baptiste to stay over the long weekend if he did not have anything special to do. After work, she took him to a bowling alley and then bar where she bought him a drink. Baptiste told her he never drank but as Sandra said there was no harm trying, he reluctantly gulped down a glass of whiskey . Shortly thereafter the alcohol went into his head. When another guy tried to chat Sandra up, stuffed some money into his jacket pocket and told him buy himself a drink, he felt so offended that he got into a brawl with the man but was beaten up. Sandra took him to a hotel room and nursed him.
The following day, two toughs who had been looking for Sandra a few times in the past several days finally tracked her down and beat her up unless she repaid the 50,000 Euros she borrowed from them. When Baptiste saw her black eye and asked her what the trouble was, she confessed, after much hesitation, that she never wanted to work as a waitress her entire life and started a restaurant of her own but it didn't work and all she succeeded in doing was being constantly hounded for repayment of her debt. As she had had enough of such harassment, she told him she would flee to Spain, where she said she got some friends. On the way, Baptiste asked her to stop by a big estate with a huge manicured garden, swimming pool, tennis court etc where he said he might be able to find someone who could help Sandra. He never told her that it was in fact his home he deserted a couple of years ago. There we learn that he used to a bright astrophysicist at university and though he was his mother's favorite son and his younger sister Liliane (Dominique Sanda)'s favorite brother, he decided suddenly that that it didn't make any sense to follow the kind of life for which he was groomed, like his elder brother, jockeying for money, power, social advancement, in short the bourgeois rat race.
He asked to see his elder brother alone and asked him to advance him 50,000 Euros from the 15% shares he had in the family company which his brother was trying list on the London Stock Exchange but told him that otherwise he did not want any share of his inheritance from his father. He was called a fool by his younger brother who said that no one ever refused an inheritance. He grabbed him by his shirt and forced him against the wall, fury in his eyes but desisted at the last minute from further violence. He got the money for Sandra and then left. Will he abandon his search for freedom which he said he so treasured? Will he quit taking only temporary teaching jobs of not more than 3 weeks? Will he finally cease his life of running away from long term commitment? Will Sandra who seems to have developed a genuine affection for him because as she said, she loved him because he always looked so sad be a sufficiently good reason for him to break his settled "new" way of life?
It's a simple story told in an unhurried pace, with well timed surprises as the events unfolded, relying for its effect entirely on the excellent quality of the performances of its two protagonists: Pierre Rochefort and Louise Bourgoin who made everything appear so "natural" and "believable", a story of two people who met in the most unlikely circumstances who somehow was fated to cross path with each other with possibly life-changing consequences. Will the felt need for a caring parent for young Mathias be a sufficiently powerful cicatrice to bond a more permanent relationship which can somehow withstand the frittering of some very real class differences or will their chance encounter on that "beautiful Sunday" remain as little more than a memory marking an ephemeral episode in the unfolding of two otherwise very different streams of lives of two very different people whose only link appear to be that both are buffeted by that unpredictible openness towards an unknowable future? It's anybody's guess.