A cantata by Mahler. It is a fairy-tale about romantic knights and a beautiful queen. The queen holds a contest for knights to win her hand in marriage. Among the many knights that compete are two brothers, one good one evil. The good one wins, but is killed before he can claim his prize. By his brother.
In the second part, a minstrel creates a flute from one of the bones of the slain brother. All it plays is the mournful story about the murder. The minstrel goes to the queen to tell her of the story, because the evil brother is claiming the prize.
In the third and last part the minstrel is playing the tune at the wedding of the queen and the evil knight. After the story comes out, the knight demands the flute, and plays it himself. He is then accused by his brother of the murder. Chaos follows, with everybody fleeing the scene and the castle crumbling.
Mahler wrote it as one of his first works, but it took thirty years to actually be performed in 1901. In those years he kept revising the music. The story is based on Der Singende Knochen (The singing bone) by the brothers Grimm. Proof that those fairy-tales were not at all that safe and happy. Grimm tales are a lot darker than Disney wants to make them.