Professor Traugott Nägler, a man with high moral standards, once repudiated his underage sister for having a baby out of wedlock.

Many years later, having a loving wife and twelve children with only the small salary of a schoolmaster, he learns that said sister has died in South America, and that he should come with his oldest yet still underage daughter, Atlanta, who was named after the ship on which the couple was married at sea by the captain.

In Uruguay, they find out that the sister had made a fortune and owned a house in Montevideo, an etablissement with several young ladies, that Atlanta inherits some money as marriage portion, and that a large amount of money could be inherited by the first underage female member in his house that behaves in the same disreputable way as the sister once did involuntarily.

Not daring to tell his daughter Atlanta about the stipulation, and definitely not her younger sisters, he is anyway tempted to make helpful suggestions to her, and especially to her suitor who had followed them secretly.

When the young couple wants to have their wedding on the same ship as her parents, they find out that size matters, and that Prof. Nägler has led a far more immoral life than his sister ever did.