The Three Ravens, which happens to be both Child Ballad #26 and Roud #5, is a Traditional English Folk Song. It was first published in 1611 in Melismata by Thomas Ravenscroft (click here for the rather good original SATB version), but the ballad is probably older. This is scored in D minor as a duet for two voices, but one could take only the top part for the melody.
As with most old traditional ballads, there are many versions of the lyrics. The two Child versions can be found at http://www.contemplator.com/child/variant26.html and there is also a nice arrangement of the ballad at http://www.contemplator.com/child/3ravens.html.
Now for the plot: In the ballad, the titular three ravens who are very, very black (like death?) are thinking about their first meal of the day. Unfortunately for them, their possible meal, a dead knight keeps being bothered by his dogs, his birds, and his pregnant wife. The wife buries the knight and dies. The ravens presumably do not get their breakfast.
(Related is Twa Corbies, the Scottish version where two crows basically celebrate how no one knows or cares where the dead knight is and how they will get a delicious meal.)
If we are to get into interpretations, it so happens that there -are- other ways to think about the ballad. Back in 1963, Vernon V. Chatman III wrote in The Three Ravens Explicated that it might not be a pregnant human wife but a dainefemme, a creature like a centaur except that it is a woman’s upper body attached to a deer’s body. I had never thought of that possibility until I read it. There are many interpretations floating about— just put “The Three Ravens” in a search engine.
If you would rather take this straightforwardly as another spooky old ballad and just get to the music, you can download your free sheet music for “The Three Ravens” as a voice duet below instead of contemplating deer-centaur-women further:
http://www.thethreeravens.com