The young worker Helena Pokorná and her widowed father are employed in the same factory. The father is spending his holidays at home in Prague and is looking forward to work. Helena is to go to the seaside for a rewarding holiday. On a hot July day, the girl rides to work in a crowded tram. On the embankment, the crowd pushes her out and Helena fails to get into several other cars. Tempted by the river, the girl calls in sick to work. She takes a steamer to Modřany. There she meets a young man who wants to sleep by the river after his night shift. Helena is drawn into the strange pastimes by a group of notorious loafers and water girls.