Agloval is the proud and arrogant duke of the seaside town of Bremervoord who is hopelessly in love with the siren, Sh'eenaz. There is one rather obvious obstacle to this love story and the prince hires Geralt to overcome it. When the witcher fails to convince the mermaid to give up her life in the ocean and join Agloval on land, the prince decides to pay him instead for investigating the mysterious deaths of several local pearl divers.
This leads to the discovery of a mysterious race of underwater dwellers. A war is narrowly averted between the people of the sea and their land-based counterparts when Sh'eenaz decides finally to give up her tail and walks to join her lover in marriage.