Lisa, a young woman living in the countryside, is going to Stockholm to meet her biological mother, Augusta Magnusson, for the first time since she was an infant. On the train she meets Holger Jönsgård, who has just finished his studies at the agricultural school in Altorp. Holger follows Lisa to her mother's dwelling on the South Side of Stockholm. Augusta is deeply moved when seeing her daughter after all those years. She and her new husband David, together with their neighbors Smulle and Klara Månsson, have prepared a crayfish party in the evening, to which both Lisa and Holger are invited. During the evening Lisa and Holger fall in love. Smulle and Klara have a beautiful daughter, Ingrid, who is courted by two young men. One of them, the wealthy Helge Hagström, lures her away in his car to a hotel outside Stockholm, where he tries to seduce her in her room by night. Ingrid resists, and back home she falls in the arms of her other wooer, the destitute Einar Hallbäck. Helge steals money from his wealthy father, and accuses Einar of the theft, thus hoping to get rid of his rival and win Lisa back.