 "The Legend of Sigurd and Gudrún", which was released worldwide on 5 May 2009 by HarperCollins and Houghton Mifflin Harcourt, retells the legend of Sigurd and the fall of the Niflungs from Germanic mythology.It is a narrative poem composed in alliterative verse and is modelled after the Old Norse poetry of the Elder Edda.Christopher Tolkien supplied copious notes and commentary upon his father's work.