A sailor, new come from the sea, sees a girl and sleeps with her. After the deed is done, they exchange names, only to find they are brother and sister. The sister stabs herself; the brother buries her and goes home grieving
Friedman states that the only recorded collection of this song was from a Scottish milkmaid in 1771. -PJS
On the scientific evidence that brothers and sisters raised apart are particularly likely to fall in love, and some further speculation as to why, see the notes to "Babylon, or, The Bonnie Banks o Fordie [Child 14]." - RBW