The Story of Kullervo

The Story of Kullervo is a prose version of the Kullervo cycle in Elias Lönnrot's Karelian and Finnish epic poem "Kalevala", written by J. R. R. Tolkien when he was an undergraduate at Exeter College, Oxford, from 1914 to 1915. That was an unsettled period for the author and this is thought to be reflected in the story's dark subject matter. 
It also marks "the first time that J. R. R. Tolkien, who had been a poet until then, began writing prose". Known as a source (among others) for Túrin Turambar, "The Story of Kullervo" was the centre of Tolkien's efforts in 1914, as he was "trying to turn one of the stories [of the "Kalevala"] — which is really a very great story and most tragic – into a short story" ("Letters", October 1914, #1). As well as Tolkien's treatment of the Kullervo cycle, the book also contains three essays: two by Tolkien from the same period and the third by Flieger – the two essays by Tolkien are (as is the story) accompanied by notes and commentary by the editor. 
The first of Tolkien's essays ("On" The Kalevala" or Land of Heroes") was written in 1914 and was delivered as a talk to the Corpus Christi College 'Sundial' club at Oxford in November 1914 and again at the Exeter College Essay Club in February 1915; his second essay ("The Kalevala"), a revised version of the first, is unfinished and is unknown to have ever been delivered. Verlyn Flieger suggests a date of circa 1919 for the revised essay; she notes but disagrees with Christina Scull & Wayne G. Hammond's estimate of 1921–24.
The main parts of the book are:
"The Story of Kullervo" was edited by Verlyn Flieger, published in 2010 in "Tolkien Studies", and republished in book form in August 2015 by HarperCollins.