François loves Anne. However, his nightshift job at the post office means they rarely get to spend much time together. One day, he sees her leaving home with her ex, Christian, who had come to break up with her for good. Reeling from the news, Anne lets François fall prey to his jealous imagination. Obsessed with the idea that she may have cheated on him, François decides to stay up all night. As he wanders, desolate, through the streets of Paris, he comes across his rival sitting in a café with a blonde-haired woman. Intrigued, he follows them. A young woman catches on to what he’s up to and accosts him in an alley of the Buttes-Chaumont.